vt: keyboard, include linux/spinlock.h

We use spin locks, but don't include linux/spinlock.h in keyboards.c. So
fix this up.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20201029113222.32640-2-jslaby@suse.czSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/vt/keyboard.c

@@ -33,6 +33,7 @@
 #include <linux/tty_flip.h>
 #include <linux/mm.h>
 #include <linux/nospec.h>
+#include <linux/spinlock.h>
 #include <linux/string.h>
 #include <linux/init.h>
 #include <linux/slab.h>