drivers/gpu/drm/radeon/radeon_cp.c: check for invalid radeon family

[Darren Jenkins <darrenrjenkins@gmail.com>]

If there is an invalid radeon family the fw_name is NULL and causes an
NULL pointer dereference.
This just adds a check for something unexpected.

Coverity CID: 13252

Signed-off-by: Darren Jenkins <darrenrjenkins@gmail.com>
diff --git a/drivers/gpu/drm/radeon/radeon_cp.c
b/drivers/gpu/drm/radeon/radeon_cp.c
index 0b2f9c2..1e66337 100644
--- a/drivers/gpu/drm/radeon/radeon_cp.c
+++ b/drivers/gpu/drm/radeon/radeon_cp.c
@@ -531,6 +531,8 @@ static int
radeon_cp_init_microcode(drm_radeon_private_t *dev_priv)
 		   ((dev_priv->flags & RADEON_FAMILY_MASK) == CHIP_RV570)) {
 		DRM_INFO("Loading R500 Microcode\n");
 		fw_name = FIRMWARE_R520;
+	} else {
+		return -EINVAL;
 	}
 
 	err = request_firmware(&dev_priv->me_fw, fw_name, &pdev->dev);