msm: vidc: Fix bug in subsystem_get error handling

On failure, subsystem_put returns an error code. Video
driver should not mistake this error code with a valid handle.

Change-Id: Ibc13adda1b2a6b64b5ae0c1fd13c179678817233
Signed-off-by: Vinay Kalia <vkalia@codeaurora.org>