drivers/gpio/pca953x.c: add a mutex to fix race condition
Add a mutex to register communication and handling. Without the mutex,
GPIOs didn't switch as expected when toggled in a fast sequence of
status changes of multiple outputs.
Signed-off-by: Roland Stigge <stigge@antcom.de> Acked-by: Eric Miao <eric.y.miao@gmail.com> Cc: Grant Likely <grant.likely@secretlab.ca> Cc: Marc Zyngier <maz@misterjones.org> Cc: Ben Gardner <bgardner@wabtec.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>