HID: picolcd: using vmalloc() requires the include of vmalloc.h

Fixes thes build errors:

drivers/hid/hid-picolcd_fb.c: In function 'picolcd_fb_destroy':
drivers/hid/hid-picolcd_fb.c:350:2: error: implicit declaration of function 'vfree' [-Werror=implicit-function-declaration]
drivers/hid/hid-picolcd_fb.c: In function 'picolcd_init_framebuffer':
drivers/hid/hid-picolcd_fb.c:508:2: error: implicit declaration of function 'vmalloc' [-Werror=implicit-function-declaration]
drivers/hid/hid-picolcd_fb.c:508:12: warning: assignment makes pointer from integer without a cast [enabled by default]
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-picolcd_fb.c

@@ -18,6 +18,7 @@
  ***************************************************************************/
 
 #include <linux/hid.h>
+#include <linux/vmalloc.h>
 #include "usbhid/usbhid.h"
 #include <linux/usb.h>