sony-laptop: fix early NULL pointer dereference

The SNC acpi driver could get early notifications before it fully
initializes and that could lead to dereferencing the sony_nc_handles
structure pointer that is still NULL at that stage.
Make sure we return early from the handle lookup function in these
cases.
Signed-off-by: Mattia Dongili <malattia@linux.it>
Signed-off-by: Matthew Garrett <mjg@redhat.com>

drivers/platform/x86/sony-laptop.c

@@ -808,6 +808,11 @@ static int sony_nc_handles_cleanup(struct platform_device *pd)
 static int sony_find_snc_handle(int handle)
 {
 	int i;
+
+	/* not initialized yet, return early */
+	if (!handles)
+		return -1;
+
 	for (i = 0; i < 0x10; i++) {
 		if (handles->cap[i] == handle) {
 			dprintk("found handle 0x%.4x (offset: 0x%.2x)\n",