msm: ADSPRPC: Map and FD non-NULL check before dereferencing

When fd is zero, we set context fds to NULL. This will avoid
calling map create for context. Proper check is required
to avoid dereferencing of map and fd.

Change-Id: Id8d4b93d7d999e14ac1ebd8291137f799a73cf1a
Acked-by: Ekansh Gupta <ekangupt@qti.qualcomm.com>
Signed-off-by: Jeya R <jeyr@codeaurora.org>