drm/radeon/dpm: fix incompatible casting on big endian

We use u16 for voltage values throughout the driver so switch
the table values to a u16 as well.  Fixes an incompatible
cast error in ci_patch_clock_voltage_limits_with_vddc_leakage()
picked up by coverity.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>