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.cz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>