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 <[e-mail]>
Signed-off-by: David Woodhouse <[e-mail]>

drivers/mtd/mtdchar.c

···
 			ret = -EROFS;
 			break;
 		case MTD_FILE_MODE_OTP_USER:
-			if (!mtd->write_user_prot_reg) {
-				ret = -EOPNOTSUPP;
-				break;
-			}
 			ret = mtd_write_user_prot_reg(mtd, *ppos, len,
 						      &retlen, kbuf);
 			break;

include/linux/mtd/mtd.h

···
 					  u_char *buf)
 {
 	*retlen = 0;
+	if (!mtd->write_user_prot_reg)
+		return -EOPNOTSUPP;
 	return mtd->write_user_prot_reg(mtd, to, len, retlen, buf);
 }