ntb: intel: fix static declaration

intel_ntb4_link_disable() missing static declaration.
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

drivers/ntb/hw/intel/ntb_hw_gen4.c

@@ -456,7 +456,7 @@ static int intel_ntb4_link_enable(struct ntb_dev *ntb,
 	return 0;
 }
 
-int intel_ntb4_link_disable(struct ntb_dev *ntb)
+static int intel_ntb4_link_disable(struct ntb_dev *ntb)
 {
 	struct intel_ntb_dev *ndev;
 	u32 ntb_cntl;