media: pms.c needs linux/slab.h

drivers/media/video/pms.c uses kzalloc() and kfree() so it should
include <linux/slab.h> to fix build errors and a warning.

  drivers/media/video/pms.c:1047:2: error: implicit declaration of function 'kzalloc'
  drivers/media/video/pms.c:1047:6: warning: assignment makes pointer from integer without a cast
  drivers/media/video/pms.c:1116:2: error: implicit declaration of function 'kfree'

Found in mmotm but applies to mainline.
Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Cc: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/media/video/pms.c

@@ -29,6 +29,7 @@
 #include <linux/ioport.h>
 #include <linux/init.h>
 #include <linux/mutex.h>
+#include <linux/slab.h>
 #include <linux/uaccess.h>
 #include <linux/isa.h>
 #include <asm/io.h>