msm: mdss: Correctly update the phy revision for 8937/8917

On 8937/8917, dsi phy revision used is 1.0. The offset to read
the phy revision is different from other chipsets. Use the
correct offset to read the phy revision from the hardware.

Change-Id: Ibcb2cbd9250751d21d4187aececbfac629f044bb
Signed-off-by: Ashish Garg <ashigarg@codeaurora.org>