[PATCH] onenand: test before subtraction on unsigned

[Roel Kluin <roel.kluin@gmail.com>]

len is unsigned so will wrap around when sizeof(struct otp_info) is greater than
len.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
---
diff --git a/drivers/mtd/onenand/onenand_base.c b/drivers/mtd/onenand/onenand_base.c
index 529af27..7c2ebe9 100644
--- a/drivers/mtd/onenand/onenand_base.c
+++ b/drivers/mtd/onenand/onenand_base.c
@@ -2296,11 +2296,12 @@ static int onenand_otp_walk(struct mtd_info *mtd, loff_t from, size_t len,
 		if (!action) {	/* OTP Info functions */
 			struct otp_info *otpinfo;
 
-			len -= sizeof(struct otp_info);
-			if (len <= 0) {
+			if (len <= sizeof(struct otp_info)) {
+				len = 0;
 				ret = -ENOSPC;
 				break;
 			}
+			len -= sizeof(struct otp_info);
 
 			otpinfo = (struct otp_info *) buf;
 			otpinfo->start = from;