msm: vidc: do not check for session supported in executing state

The v4l2 video driver should check if the video session is supported
only prior to entering the executing state. Once video session is
in executing state, the session should be always honored.

Change-Id: Iaa59089ef05f03bbc821af8c7fd4fbc342067b3a
Signed-off-by: Arun Menon <avmenon@codeaurora.org>