Revert "env: sf: fix environment in SPI NOR"

Per Heiko the original changes were correct and something is misbehaving
on his hardware.

This reverts commit 3d5931e5986a49c44cdab845c6751d845812e8d8.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/env/sf.c b/env/sf.c
index 31dd003..b3dec82 100644
--- a/env/sf.c
+++ b/env/sf.c
@@ -98,7 +98,7 @@
 	u32 addr = 0;
 	u32 page_size = flash->page_size;
 
-	memset(buf, 0xff, len);
+	memset(buf, 0x0, len);
 	for (int i = 0; i < len / page_size; ++i) {
 		int ret = spi_flash_read(flash, offset, page_size,
 					 &((char *)buf)[addr]);