msm: kgsl: Don't block on the dispatcher mutex in issuecmds

Don't block the rendering thread if we can't get our hands on the
dispatcher mutex in adreno_dispatcher_issuecmds(). If the mutex
is held then there is an excellent chance that somebody else is
running the scheduler. To be 100% sure schedule the worker again
to catch any subtle races.

Change-Id: Ic0dedbad8126ebfe776840cd6d7227b39477f3fa
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>