drm/radeon: gcc fixes for rv6xx dpm

Newer versions of gcc seem to wander off into the
weeds when dealing with variable sizes arrays in
structs.  Rather than indexing the arrays, use
pointer arithmetic.

See bugs:
https://bugs.freedesktop.org/show_bug.cgi?id=66932
https://bugs.freedesktop.org/show_bug.cgi?id=66972
https://bugs.freedesktop.org/show_bug.cgi?id=66945

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

drivers/gpu/drm/radeon/rv6xx_dpm.c

@@ -1918,6 +1918,7 @@ static int rv6xx_parse_power_table(struct radeon_device *rdev)
 			 (power_state->v1.ucNonClockStateIndex *
 			  power_info->pplib.ucNonClockSize));
 		if (power_info->pplib.ucStateEntrySize - 1) {
+			u8 *idx;
 			ps = kzalloc(sizeof(struct rv6xx_ps), GFP_KERNEL);
 			if (ps == NULL) {
 				kfree(rdev->pm.dpm.ps);
@@ -1926,12 +1927,12 @@ static int rv6xx_parse_power_table(struct radeon_device *rdev)
 			rdev->pm.dpm.ps[i].ps_priv = ps;
 			rv6xx_parse_pplib_non_clock_info(rdev, &rdev->pm.dpm.ps[i],
 							 non_clock_info);
+			idx = (u8 *)&power_state->v1.ucClockStateIndices[0];
 			for (j = 0; j < (power_info->pplib.ucStateEntrySize - 1); j++) {
 				clock_info = (union pplib_clock_info *)
 					(mode_info->atom_context->bios + data_offset +
 					 le16_to_cpu(power_info->pplib.usClockInfoArrayOffset) +
-					 (power_state->v1.ucClockStateIndices[j] *
-					  power_info->pplib.ucClockInfoSize));
+					 (idx[j] * power_info->pplib.ucClockInfoSize));
 				rv6xx_parse_pplib_clock_info(rdev,
 							     &rdev->pm.dpm.ps[i], j,
 							     clock_info);