camera2: (legacy) Fix the comparison for fixed-focus cameras

* Use #equals instead of == for string comparison
* Also make sure lens.info.minimumFocusDistance shows up in
  CameraCharacteristics#getKeys() for fixed-focus cameras

Bug: 16900875
Change-Id: I3b9248c5cb62ddcfb13587c6349525e145e353ac
1 file changed