media video cx23888 driver: ported to new kfifo API

Fix the cx23888 driver to use the new kfifo API.  Using kfifo_reset()
may result in a possible race conditions.  This patch fixes it by using
a spinlock around the kfifo_reset() function.

Signed-off-by: Stefani Seibold <stefani@seibold.net>
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
Reviewed-by: Andy Walls <awalls@radix.net>
Acked-by: Andy Walls <awalls@radix.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>