drm/radeon/dpm: fix a typo in the rv6xx mclk setup

Need to set high for the last two entries.  Looks
like a copy and paste typo.
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/rv6xx_dpm.c

@@ -819,7 +819,7 @@ static void rv6xx_program_memory_timing_parameters(struct radeon_device *rdev)
 		 POWERMODE1(calculate_memory_refresh_rate(rdev,
 							  pi->hw.sclks[R600_POWER_LEVEL_MEDIUM])) |
 		 POWERMODE2(calculate_memory_refresh_rate(rdev,
-							  pi->hw.sclks[R600_POWER_LEVEL_MEDIUM])) |
+							  pi->hw.sclks[R600_POWER_LEVEL_HIGH])) |
 		 POWERMODE3(calculate_memory_refresh_rate(rdev,
 							  pi->hw.sclks[R600_POWER_LEVEL_HIGH])));
 	WREG32(ARB_RFSH_RATE, arb_refresh_rate);