drm/radeon/kms: fix legacy LVDS dpms sequence

Add delay after turning off the LVDS encoder.

Fixes:
https://bugzilla.kernel.org/show_bug.cgi?id=16389

Tested-by: Jan Kreuzer <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>
Cc: [e-mail]
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/radeon/radeon_legacy_encoders.c

···
 		udelay(panel_pwr_delay * 1000);
 		WREG32(RADEON_LVDS_GEN_CNTL, lvds_gen_cntl);
 		WREG32_PLL(RADEON_PIXCLKS_CNTL, pixclks_cntl);
+		udelay(panel_pwr_delay * 1000);
 		break;
 	}