msm: msm_bus: Suspected fix for deadlock

mutex is not released while checking for
null pdata which can lead to possible deadlock
condition.

Change-Id: I1dc3efd725df5bb75c96434a81d9a8f3f868cd0a
Signed-off-by: Alok Chauhan <alokc@codeaurora.org>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>