mtd: Rename free() to rfree()

This function name conflicts with our desire to #define free() to
something else on sandbox. Since it deals with resources, rename it to
rfree().

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mtd/nand/spi/winbond.c b/drivers/mtd/nand/spi/winbond.c
index 6ba8bc5..de9352e 100644
--- a/drivers/mtd/nand/spi/winbond.c
+++ b/drivers/mtd/nand/spi/winbond.c
@@ -59,7 +59,7 @@
 
 static const struct mtd_ooblayout_ops w25m02gv_ooblayout = {
 	.ecc = w25m02gv_ooblayout_ecc,
-	.free = w25m02gv_ooblayout_free,
+	.rfree = w25m02gv_ooblayout_free,
 };
 
 static int w25m02gv_select_target(struct spinand_device *spinand,