drm/amdgpu: fix NULL pointer dereference for Renoir

Commit c1cf79ca5ced46 ("drm/amdgpu: use IP discovery table for renoir")
introduced a NULL pointer dereference when booting with
amdgpu.discovery=0, because it removed the call of vega10_reg_base_init()
for that case.

Fix this by calling that funcion if amdgpu_discovery == 0 in addition to
the case that amdgpu_discovery_reg_base_init() failed.

Fixes: c1cf79ca5ced46 ("drm/amdgpu: use IP discovery table for renoir")
Signed-off-by: Dirk Gouders <[e-mail]>
Cc: Hawking Zhang <[e-mail]>
Cc: Evan Quan <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/soc15.c

···
 		 * it doesn't support SRIOV. */
 		if (amdgpu_discovery) {
 			r = amdgpu_discovery_reg_base_init(adev);
-			if (r) {
-				DRM_WARN("failed to init reg base from ip discovery table, "
-					 "fallback to legacy init method\n");
-				vega10_reg_base_init(adev);
-			}
+			if (r == 0)
+				break;
+			DRM_WARN("failed to init reg base from ip discovery table, "
+				 "fallback to legacy init method\n");
 		}
+		vega10_reg_base_init(adev);
 		break;
 	case CHIP_VEGA20:
 		vega20_reg_base_init(adev);