mmc: host: Use sentinels for devicetree match tables

Use sentinels as the path terminator for device match table
in drivers msm_sdcc.c and sdhci-msm.c. Without this, of_dev_lookup()
may run off the end of the array looking for bogus data.

CRs-Fixed: 582113
Change-Id: I069d3e058cea9f1bf74d48e7f7e83465ca981017
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>