mfd: Fix menelaus mmc slot 2 misconfiguration

We are modifying register value instead of return value.

This fix is originally done by Carlos Eduardo Aguiar. Original fix is
commit bb4e91722e29efe31587d2cc664b6def645aecd9 in
git.kernel.org/pub/scm/linux/kernel/git/tmlind/linux-omap-2.6.git

Author modified the fix for mainline version of menelaus.

Signed-off-by: Jarkko Nikula <jhnikula@gmail.com>
Cc: Carlos Eduardo Aguiar <carlos.aguiar@indt.org.br>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>