firmware: fix google/gsmi.c build warning

Modify function parameter type to match expected type.  Fixes a
build warning:

drivers/firmware/google/gsmi.c:473: warning: initialization from incompatible pointer type

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Cc: Mike Waychison <mikew@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>