mmc: sdhci: Fix race between runtime suspend and detect work

When the card is removed in mmc_sd_detect(), the card status is
marked as runtime suspended and this asynchronously triggers
runtime suspend of it's parent mmc_host class device. The
mmc_power_off() will be called from runtime suspend handler and
it races with mmc_power_off() within mmc_sd_detect(). Fix this by
acquiring mutex at the host driver when set_ios host operation
is invoked and until it is done.

CRs-fixed: 513141
Change-Id: I4e7afbe966ecbcc2c8bf746fb6cffc64b7cf252e
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>