efivars: Mark local function as static

This fixes the following sparse warning
drivers/firmware/efi/efivars.c:567:6: warning: symbol 'efivars_sysfs_exit' was not declared. Should it be static?
Signed-off-by: Bojan Prtvar <prtvar.b@gmail.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

drivers/firmware/efi/efivars.c

@@ -564,7 +564,7 @@ static int efivar_sysfs_destroy(struct efivar_entry *entry, void *data)
 	return 0;
 }
 
-void efivars_sysfs_exit(void)
+static void efivars_sysfs_exit(void)
 {
 	/* Remove all entries and destroy */
 	__efivar_entry_iter(efivar_sysfs_destroy, &efivar_sysfs_list, NULL, NULL);