mfd: Add missing out of memory check for pcf50633

Resolves-bug: https://bugzilla.kernel.org/show_bug.cgi?id=44561


Reported-by:  <rucsoftsec@gmail.com>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>