opae.admin: mtd: change `open` to return `self`
This allows using it in a context manager:
```Python
mtd_obj = mtd('/dev/mtd0')
with mtd_obj.open('r') as m:
# do stuff with m
@@ -60,6 +60,7 @@ class mtd(loggable):
self.log.warn('device is currently open, closing')
self._fp.close()
self._fp = open(self._devpath, mode)
+ return self
def close(self):
"""close Close an open mtd device."""
