mtd: physmap_of: fix null pointer deference when kzalloc returns null

static analysis by smatch caught the following error:

drivers/mtd/maps/physmap_of.c:135 of_get_probes()
   error: potential null dereference 'res'.  (kzalloc returns null)

Check for failed kzalloc and return -ENOMEM in of_flash_probe if
this occurs.
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NBrian Norris <computersforpeace@gmail.com>

drivers/mtd/maps/physmap_of.c

@@ -130,6 +130,8 @@ static const char * const *of_get_probes(struct device_node *dp)
 			count++;
 
 	res = kzalloc((count + 1)*sizeof(*res), GFP_KERNEL);
+	if (!res)
+		return NULL;
 	count = 0;
 	while (cplen > 0) {
 		res[count] = cp;
@@ -311,6 +313,10 @@ static int of_flash_probe(struct platform_device *dev)
 
 	ppdata.of_node = dp;
 	part_probe_types = of_get_probes(dp);
+	if (!part_probe_types) {
+		err = -ENOMEM;
+		goto err_out;
+	}
 	mtd_device_parse_register(info->cmtd, part_probe_types, &ppdata,
 			NULL, 0);
 	of_free_probes(part_probe_types);