msm: Add null pointer checks

Add null pointer checks to ensure subsystem API calls
do not dereferences null pointers and cause system
crash.

Change-Id: I5d5efc21b346ac5b9f6ddb2e42354aaf40fb56a7
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>

Conflicts:

	arch/arm/mach-msm/subsystem_map.c