msm: camera: eeprom: set platform driver data to null

when kfree is called on ectrl structure during
driver remove, there is a dangling pointer left
in platform driver data and v4l2 subdevice.
This change will assign these dangling pointers
to NULL.

Change-Id: If65ac2b5f6ac55a274df223ff4ea1b449c0809cf
Signed-off-by: Vishalsingh Hajeri <vhajeri@codeaurora.org>