ARM: dts: msm: Change SPI opeartional frequency on 8916

UICC a SPI client can operate at 50MHz, to achieve the
maximum throughput changing  maximum supported frequency
to 50MHz.

CRs-Fixed: 647032
Change-Id: Ic4f4224eb95187b48e292c068cbbf45322f54d78
Signed-off-by: Sana Venkat Raju <c_vsana@codeaurora.org>