drm/radeon: fix ordering in pll picking on dce4+

No functional change, but re-order the cases so they
evaluate properly due to the way the DCE macros work.

Noticed by kallisti5 on IRC.
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/atombios_crtc.c

@@ -1531,12 +1531,12 @@ static int radeon_atom_pick_pll(struct drm_crtc *crtc)
 				 * crtc virtual pixel clock.
 				 */
 				if (ENCODER_MODE_IS_DP(atombios_get_encoder_mode(test_encoder))) {
-					if (ASIC_IS_DCE5(rdev))
-						return ATOM_DCPLL;
+					if (rdev->clock.dp_extclk)
+						return ATOM_PPLL_INVALID;
 					else if (ASIC_IS_DCE6(rdev))
 						return ATOM_PPLL0;
-					else if (rdev->clock.dp_extclk)
-						return ATOM_PPLL_INVALID;
+					else if (ASIC_IS_DCE5(rdev))
+						return ATOM_DCPLL;
 				}
 			}
 		}