drm/amdgpu: fix a vcn4 boot poll bug in emulation mode

The return value should be set in vcn4 boot poll.
Signed-off-by: Sonny Jiang <sonny.jiang@amd.com>
Reviewed-by: James Zhu <James.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/vcn_v4_0.c

@@ -1041,6 +1041,7 @@ static int vcn_v4_0_start(struct amdgpu_device *adev)
 			}
 
 			if (amdgpu_emu_mode==1) {
+				r = -1;
 				if (status & 2) {
 					r = 0;
 					break;