drm/amdgpu: fix NULL pointer dereference for Renoir

Commit c1cf79ca ("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: c1cf79ca ("drm/amdgpu: use IP discovery table for renoir")
Signed-off-by: Dirk Gouders <dirk@gouders.net>
Cc: Hawking Zhang <Hawking.Zhang@amd.com>
Cc: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -662,12 +662,12 @@ static void soc15_reg_base_init(struct amdgpu_device *adev)
 		 * 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);