Rename mCursorDrawble to mDrawableForCursor

To go around app bugs caused by assuming that mCursorDrawable is an
array. The apps try to manipulate mCursorDrawable by using
reflection, but crash since they access it incorrectly after it
changed from an array to a single Drawable in
I249befaf70630bef435c8db9039e8aacf233bf7c.

Bug: 66988832
Test: mmm -j frameworks/base
Change-Id: I04fc930d786dd4c74b560d7a25d17353f49ea25b