mfd: db8500-prcmu tweak for modem wakeup

This is a tweak for the case where the modem goes to sleep while
emitting the AC_WAKE_ACK anyway. Also print the modem errors as
critical, since they jeopardize the entire platform when they
occur.

Signed-off-by: Mattias Nilsson <mattias.i.nilsson@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>