Fix buffer overflow in exynos5_ehci

Use proper size of exynos_ehci_softc, not the generic one.

Reviewed by:   andrew
Submitted by:  Wojciech Macek <wma@semihalf.com>
Obtained from: Semihalf
Sponsored by:  Juniper Networks Inc.
Differential Revision: https://reviews.freebsd.org/D4189

sys/arm/samsung/exynos/exynos5_ehci.c

@@ -122,7 +122,7 @@ static device_method_t ehci_methods[] = {
 static driver_t ehci_driver = {
 	"ehci",
 	ehci_methods,
-	sizeof(ehci_softc_t)
+	sizeof(struct exynos_ehci_softc)
 };
 
 static devclass_t ehci_devclass;