mmc: msm_sdcc: prevent possible NULL pointer access

mmc_signal_sdio_irq() should only be called if SDIO interrupt is
received for SDIO card. If mmc_signal_sdio_irq() function is called
when card is not present or for non-SDIO card, it may result into
NULL pointer access (due to uninitialized spin lock access) inside
mmc_signal_sdio_irq() function.

This change fixes the above issue by adding relevant safety checks in
driver.

CRs-Fixed: 423795
Change-Id: I1829acd81f91b4d0e01d509dd9e0926547cec7a0
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>