mtd: spi-nor-core: Don't overwrite return value if it is non-zero

The cleanup code of the spi_nor_erase() function overwrites the ret
variable with return value of clean_bar(), even if the ret variable is
already set. Fix this.

Signed-off-by: Marek BehĂșn <marek.behun@nic.cz>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>
diff --git a/drivers/mtd/spi/spi-nor-core.c b/drivers/mtd/spi/spi-nor-core.c
index 6231ec5..d8eed59 100644
--- a/drivers/mtd/spi/spi-nor-core.c
+++ b/drivers/mtd/spi/spi-nor-core.c
@@ -909,7 +909,7 @@
 {
 	struct spi_nor *nor = mtd_to_spi_nor(mtd);
 	u32 addr, len, rem;
-	int ret;
+	int ret, err;
 
 	dev_dbg(nor->dev, "at 0x%llx, len %lld\n", (long long)instr->addr,
 		(long long)instr->len);
@@ -949,7 +949,9 @@
 
 erase_err:
 #ifdef CONFIG_SPI_FLASH_BAR
-	ret = clean_bar(nor);
+	err = clean_bar(nor);
+	if (!ret)
+		ret = err;
 #endif
 	write_disable(nor);