mmc: msm_sdcc: fix possible corruption of MASK0 register

msmsdcc_enable_sdio_irq() can be called in interrupt context
in host driver and process context from core layer in which
only "enable" is protected by host lock. There is a possible
race between sdio_irq_thread() enabling the operational interrupt
and mmc_signal_sdio_irq() (in mmc_sdio_resume()) disabling it.
This can cause the SDIO operational interrupt to be disabled
and lead to receive stalls temporarily.

Change-Id: I58aa8da89c68dae40f192bc1e9538048c43fe738
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>