ARM: dts: msm: Update clock phandle for GFX SMMU on msmtitatnium

Clock phandle has been updated and we need to use
clock_gcc_gfx instead of clock_gcc. Make the
corresponding change for GFX SMMU device node.

Change-Id: Iad22311f632e3bfc9f160b0501b78f9a3a238599
Signed-off-by: Susheel Khiani <skhiani@codeaurora.org>