sf: stmicro: use common page timeout define

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
CC: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
diff --git a/drivers/mtd/spi/stmicro.c b/drivers/mtd/spi/stmicro.c
index e401cd0..b43e9f4 100644
--- a/drivers/mtd/spi/stmicro.c
+++ b/drivers/mtd/spi/stmicro.c
@@ -295,8 +295,7 @@
 			break;
 		}
 
-		/* Up to 2 seconds */
-		ret = stmicro_wait_ready(flash, 2 * CONFIG_SYS_HZ);
+		ret = stmicro_wait_ready(flash, SPI_FLASH_PAGE_ERASE_TIMEOUT);
 		if (ret < 0) {
 			debug("SF: STMicro page erase timed out\n");
 			break;