mtd: mtd->write_user_prot_reg directly

Instead, just call 'mtd_write_user_prot_reg()' and check the '-EOPNOTSUPP' return
code.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index e488cf9..7cd56d2 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -381,6 +381,8 @@
 					  u_char *buf)
 {
 	*retlen = 0;
+	if (!mtd->write_user_prot_reg)
+		return -EOPNOTSUPP;
 	return mtd->write_user_prot_reg(mtd, to, len, retlen, buf);
 }