spi_flash: support old STMicro parts with RES

Some old STMicro parts do not support JEDEC ID (0x9f). This patch
uses RES (0xab) to get Electronic ID and translates it to JEDEC ID.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Acked-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/drivers/mtd/spi/spi_flash.c b/drivers/mtd/spi/spi_flash.c
index 612f819..dd0dbbf 100644
--- a/drivers/mtd/spi/spi_flash.c
+++ b/drivers/mtd/spi/spi_flash.c
@@ -147,6 +147,7 @@
 #endif
 #ifdef CONFIG_SPI_FLASH_STMICRO
 	case 0x20:
+	case 0xff: /* Let the stmicro func handle non-JEDEC ids */
 		flash = spi_flash_probe_stmicro(spi, idcode);
 		break;
 #endif