mfd: Fix ucb1x00 build failure for collie_defconfig

This patch fixes a build failure[1], by adding the missing semaphore.h include

References:
[1] http://kisskb.ellerman.id.au/kisskb/buildresult/2234322/

Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>