msm: ADSPRPC: Fix deadlock during SSR

Deadlock is happening because map_mutex and smd_mutex lock is
acquired before fastrpc_mmap_remove_ssr() call and inside again
in get_args() and fastrpc_invoke_send() respectively. Added
lock only to critical sections in need.

Change-Id: I900e44790ec0285b7b156542bf599092479dc864
Signed-off-by: Vamsi krishna Gattupalli <vgattupa@codeaurora.org>