staging: nvec: Include missing headers

Those headers were apparently included by other headers
previously, but are not anymore.

Signed-off-by: Julian Andres Klode <[e-mail]>
Acked-by: Marc Dietrich <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/nvec/nvec.h

···
 #ifndef __LINUX_MFD_NVEC
 #define __LINUX_MFD_NVEC
 
+#include <linux/notifier.h>
 #include <linux/semaphore.h>
 
 typedef enum {

drivers/staging/nvec/nvec_kbd.c

···
+#include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/input.h>
 #include <linux/delay.h>

drivers/staging/nvec/nvec_ps2.c

···
+#include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/serio.h>
 #include <linux/delay.h>