BUG:pd.value_counts() When the values are equal, the order of equal values is invalid
```python
import pandas as pd
df = pd.DataFrame([('a', 1), ('b', 1), ('c', 3), ('a', 1), ('b', 1)])
print(pd.value_counts(df[0], sort=True))
# you can see two situations
# b    2
# a    2
# c    1
# Name: 0, dtype: int64
# a    2
# b    2
# c    1
# Name: 0, dtype: int64
```

#### Problem description

When the values are equal, the order of equal values is invalid, Sorting is only for values, no index is processed

#### Expected Output

INSTALLED VERSIONS
------------------
commit           : None
python           : 3.7.4.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 19.4.0
machine          : x86_64
processor        : i386
byteorder        : little
LC_ALL           : None
LANG             : None
LOCALE           : zh_CN.UTF-8

pandas           : 1.0.3
numpy            : 1.18.4
pytz             : 2020.1
dateutil         : 2.8.1
pip              : 20.1
setuptools       : 46.1.3
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : None
IPython          : None
pandas_datareader: None
bs4              : None
bottleneck       : None
fastparquet      : None
gcsfs            : None
lxml.etree       : None
matplotlib       : 3.2.1
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pytables         : None
pytest           : None
pyxlsb           : None
s3fs             : None
scipy            : 1.4.1
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
xlsxwriter       : None
numba            : None
None

</details>
