drm/radeon/atom: workaround vbios bug in transmitter table on rs780

Some rs780 asics seem to be affected as well.

See:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=91f3a6aaf280294b07c05dfe606e6c27b7ba3c72

Fixes:
https://bugzilla.kernel.org/show_bug.cgi?id=60791

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

drivers/gpu/drm/radeon/atombios_encoders.c

@@ -1655,7 +1655,7 @@ radeon_atom_encoder_dpms_dig(struct drm_encoder *encoder, int mode)
 			 * does the same thing and more.
 			 */
 			if ((rdev->family != CHIP_RV710) && (rdev->family != CHIP_RV730) &&
-			    (rdev->family != CHIP_RS880))
+			    (rdev->family != CHIP_RS780) && (rdev->family != CHIP_RS880))
 				atombios_dig_transmitter_setup(encoder, ATOM_TRANSMITTER_ACTION_ENABLE_OUTPUT, 0, 0);
 		}
 		if (ENCODER_MODE_IS_DP(atombios_get_encoder_mode(encoder)) && connector) {