mtd: mchp48l640: silence some uninitialized variable warnings

Smatch complains that zero length read/writes will lead to an
uninitalized return value.  I don't know if that's possible, but
it's nicer to return a zero literal anyway so let's do that.

Fixes: 88d1250 ("mtd: devices: add support for microchip 48l640 EERAM")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/YMyir961W28TX5dT@mwanda

drivers/mtd/devices/mchp48l640.c

@@ -229,7 +229,7 @@ static int mchp48l640_write(struct mtd_info *mtd, loff_t to, size_t len,
 		woff += ws;
 	}
 
-	return ret;
+	return 0;
 }
 
 static int mchp48l640_read_page(struct mtd_info *mtd, loff_t from, size_t len,
@@ -286,7 +286,7 @@ static int mchp48l640_read(struct mtd_info *mtd, loff_t from, size_t len,
 		woff += ws;
 	}
 
-	return ret;
+	return 0;
 };
 
 static const struct mchp48_caps mchp48l640_caps = {