sf: unify write disable commands

Every spi flash uses the same write disable command, so unify this in
the common code.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Fixed commit message.
Signed-off-by: Wolfgang Denk <wd@denx.de>

drivers/mtd/spi/spi_flash_internal.h

@@ -20,6 +20,7 @@
 #define CMD_READ_ARRAY_LEGACY		0xe8
 
 #define CMD_PAGE_PROGRAM		0x02
+#define CMD_WRITE_DISABLE		0x04
 #define CMD_READ_STATUS			0x05
 #define CMD_WRITE_ENABLE		0x06
 
@@ -61,6 +62,14 @@ static inline int spi_flash_cmd_write_enable(struct spi_flash *flash)
 	return spi_flash_cmd(flash->spi, CMD_WRITE_ENABLE, NULL, 0);
 }
 
+/*
+ * Disable writing on the SPI flash.
+ */
+static inline int spi_flash_cmd_write_disable(struct spi_flash *flash)
+{
+	return spi_flash_cmd(flash->spi, CMD_WRITE_DISABLE, NULL, 0);
+}
+
 /*
  * Same as spi_flash_cmd_read() except it also claims/releases the SPI
  * bus. Used as common part of the ->read() operation.

drivers/mtd/spi/sst.c

@@ -105,7 +105,7 @@ sst_enable_writing(struct spi_flash *flash)
 static int
 sst_disable_writing(struct spi_flash *flash)
 {
-	int ret = spi_flash_cmd(flash->spi, CMD_SST_WRDI, NULL, 0);
+	int ret = spi_flash_cmd_write_disable(flash);
 	if (ret)
 		debug("SF: Disabling Write failed\n");
 	return ret;