[media] pms: fix build error in pms_probe()

Fix a compiler breakage introduced by commit 8173090a:

drivers/media/video/pms.c: In function ‘pms_probe’:
drivers/media/video/pms.c:1047:2: error: implicit declaration of function ‘kzalloc’ [-Werror=implicit-function-declaration]
drivers/media/video/pms.c:1116:2: error: implicit declaration of function ‘kfree’ [-Werror=implicit-function-declaration]
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/pms.c

@@ -26,6 +26,7 @@
 #include <linux/fs.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
+#include <linux/slab.h>
 #include <linux/ioport.h>
 #include <linux/init.h>
 #include <linux/mutex.h>