ARM: 7714/1: mmc: mmci: Ensure return value of regulator_enable() is checked

This patch suppresses the warning below:

drivers/mmc/host/mmci.c: In function ‘mmci_set_ios’:
drivers/mmc/host/mmci.c:1165:20: warning: ignoring return value of
        ‘regulator_enable’, declared with attribute warn_unused_result
        [-Wunused-result]

Cc: Chris Ball <cjb@laptop.org>
Acked-by: Srinidhi Kasagar <srinidhi.kasagar@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>