ARM: dts: msm: reduce VDD_GFX CPR max aging adjustment for msm8996v3

Reduce the VDD_GFX CPR max aging adjustment from 25 mV to 15 mV.
Aging characterization has shown that at most 15 mV of additional
supply voltage is required as the device ages.

Change-Id: Ia96ff89afea16df6bfae9471a65dbf1a421b3f45
Signed-off-by: David Collins <collinsd@codeaurora.org>