msm: camera: Check if client is NULL before calling ion_free

NULL check was added inorder to prevent a target reboot in ion_free
in case client is already NULL

Change-Id: I263f56ff06ad7907c459b4f7254fc1435a41c61d
Signed-off-by: Aditya Jonnalagadda <ajonnala@codeaurora.org>
Signed-off-by: task650 <task650@gmail.com>

Conflicts:
	drivers/media/video/videobuf2-msm-mem.c