msm:ADSPRPC :Fix to avoid Use after free in fastrpc_internal_munmap

Added a check to validate map before freeing it to avoid Use after
free scenario.

Change-Id: Ic723a4fe964a4909119663500018f2a07976105b
Signed-off-by: Vamsi krishna Gattupalli <vgattupa@codeaurora.org>
1 file changed