drm/amd/pm: Fix missing prototype warning

Fix below warning
warning: no previous prototype for '__smu_get_enabled_features' [-Wmissing-prototypes]

Fixes: f141e251 ("drm/amd/pm: validate SMU feature enable message for getting feature enabled mask")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/pm/swsmu/smu_cmn.c

@@ -523,7 +523,7 @@ int smu_cmn_feature_is_supported(struct smu_context *smu,
 	return test_bit(feature_id, feature->supported);
 }
 
-int __smu_get_enabled_features(struct smu_context *smu,
+static int __smu_get_enabled_features(struct smu_context *smu,
 			       uint64_t *enabled_features)
 {
 	return smu_cmn_call_asic_func(get_enabled_mask, smu, enabled_features);