sandbox: spi: Remove an incorrect free()

We must not free data that is managed by driver mode. Remove this line,
which is a hangover from the pre-driver-model code.

This fixes a problem where 'sf probe' crashes U-Boot if the backing file
for the SPI flash cannot be found.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jagan Teki <jteki@openedev.com>
Tested-by: Jagan Teki <jteki@openedev.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

drivers/mtd/spi/sandbox.c

@@ -187,7 +187,6 @@ static int sandbox_sf_probe(struct udevice *dev)
 
 	sbsf->fd = os_open(pdata->filename, 02);
 	if (sbsf->fd == -1) {
-		free(sbsf);
 		printf("%s: unable to open file '%s'\n", __func__,
 		       pdata->filename);
 		ret = -EIO;