drm/amdgpu: fix no previous prototype warning

add static prefix for vangogh_set_apu_thermal_limit function
Signed-off-by: Kun Liu <Kun.Liu2@amd.com>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202303010827.c2N0yBGT-lkp@intel.comReviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/pm/swsmu/smu11/vangogh_ppt.c

@@ -1597,7 +1597,7 @@ static int vangogh_get_apu_thermal_limit(struct smu_context *smu, uint32_t *limi
 					      0, limit);
 }
 
-int vangogh_set_apu_thermal_limit(struct smu_context *smu, uint32_t limit)
+static int vangogh_set_apu_thermal_limit(struct smu_context *smu, uint32_t limit)
 {
 	return smu_cmn_send_smc_msg_with_param(smu,
 					      SMU_MSG_SetReducedThermalLimit,