REGR: Sorted pandas series is not plotted in the expected order in pandas 1.2.0
- [x] I have checked that this issue has not already been reported.

- [x] I have confirmed this bug exists on the latest version of pandas.

- [ ] (optional) I have confirmed this bug exists on the master branch of pandas.

---

#### Code Sample
Note: The code was executed in Jupyter notebook.

```
import pandas as pd
print(pd.__version__)
d = {'col1': [4,2,3,1]}
df = pd.DataFrame(data=d)
df['col1'].sort_values().plot(kind='bar')
```

#### Problem description

In Pandas 1.2.0, the sorted values are not plotted in the correct order. Note that ```df['col1'].sort_values()``` does return sorted values.

![pandas 1.2.0](https://user-images.githubusercontent.com/25637736/103424892-eb430d00-4b7c-11eb-999d-0e525d122776.png)

#### Expected Output

In Pandas 1.1.5, this works as expected. This might be the case in older versions of pandas as well.

![pandas 1.1.5](https://user-images.githubusercontent.com/25637736/103424905-001fa080-4b7d-11eb-9577-0ff812d6d6fe.png)

#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit           : b5958ee1999e9aead1938c0bba2b674378807b3d
python           : 3.8.5.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 20.2.0
Version          : Darwin Kernel Version 20.2.0: Wed Dec  2 20:39:59 PST 2020; root:xnu-7195.60.75~1/RELEASE_X86_64
machine          : x86_64
processor        : i386
byteorder        : little
LC_ALL           : None
LANG             : en_CA.UTF-8
LOCALE           : en_CA.UTF-8

pandas           : 1.1.5
numpy            : 1.19.1
pytz             : 2020.1
dateutil         : 2.8.1
pip              : 20.2.4
setuptools       : 50.3.0.post20201006
Cython           : 0.29.21
pytest           : 6.1.1
hypothesis       : 5.37.4
sphinx           : 3.2.1
blosc            : None
feather          : None
xlsxwriter       : 1.3.7
lxml.etree       : 4.6.1
html5lib         : 1.1
pymysql          : None
psycopg2         : None
jinja2           : 2.11.2
IPython          : 7.18.1
pandas_datareader: None
bs4              : 4.9.3
bottleneck       : 1.3.2
fsspec           : 0.8.3
fastparquet      : None
gcsfs            : None
matplotlib       : 3.3.2
numexpr          : 2.7.1
odfpy            : None
openpyxl         : 3.0.5
pandas_gbq       : None
pyarrow          : None
pytables         : None
pyxlsb           : None
s3fs             : None
scipy            : 1.5.0
sqlalchemy       : 1.3.19
tables           : 3.6.1
tabulate         : None
xarray           : None
xlrd             : 1.2.0
xlwt             : 1.3.0
numba            : 0.51.2
</details>