x38_edac: Make a local function static

Make a local function static in order to fix the following sparse
warning:

drivers/edac/x38_edac.c:252:14: warning: symbol 'x38_map_mchbar' was not declared. Should it be static?
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
[ Boris: Correct commit message ]
Signed-off-by: Borislav Petkov <bp@suse.de>

drivers/edac/x38_edac.c

@@ -248,8 +248,7 @@ static void x38_check(struct mem_ctl_info *mci)
 	x38_process_error_info(mci, &info);
 }
 
-
-void __iomem *x38_map_mchbar(struct pci_dev *pdev)
+static void __iomem *x38_map_mchbar(struct pci_dev *pdev)
 {
 	union {
 		u64 mchbar;