Platform: OLPC: Fix olpc_xo175_ec_cmd() return value

Reset the ret variable to make sure it olpc_xo175_ec_cmd() ends up
returning zero on success.

Fixes: 0c3d931b ("Platform: OLPC: Add XO-1.75 EC driver")
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/platform/olpc/olpc-xo175-ec.c

@@ -507,6 +507,7 @@ static int olpc_xo175_ec_cmd(u8 cmd, u8 *inbuf, size_t inlen, u8 *resp,
 		nr_bytes = resp_len;
 	} else {
 		nr_bytes = (size_t)ret;
+		ret = 0;
 	}
 	resp_len = min(resp_len, nr_bytes);