phy: keystone-usb: Do not negate return code

In keystone_usb_init the return code from psc_enable_module should be
returned as is rather than being negated.

This issue was found by Smatch.

Signed-off-by: Andrew Goodbody <andrew.goodbody@linaro.org>

drivers/phy/keystone-usb-phy.c

@@ -41,7 +41,7 @@ static int keystone_usb_init(struct phy *phy)
 	rc = psc_enable_module(keystone->psc_domain);
 	if (rc) {
 		debug("Cannot enable USB module");
-		return -rc;
+		return rc;
 	}
 	mdelay(10);