drivers/usb/host/ehci-fsl.c: Fix GCC 4.6 build warning

Fix:

ehci-fsl.c: In function 'ehci_hcd_init':
ehci-fsl.c:43:7: warning: variable 'usb_phy' set but not used [-Wunused-but-set-variable]

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

drivers/usb/host/ehci-fsl.c

@@ -40,11 +40,13 @@
 int ehci_hcd_init(void)
 {
 	struct usb_ehci *ehci;
-	char usb_phy[5];
 	const char *phy_type = NULL;
 	size_t len;
+#ifdef CONFIG_SYS_FSL_USB_INTERNAL_UTMI_PHY
+	char usb_phy[5];
 
 	usb_phy[0] = '\0';
+#endif
 
 	ehci = (struct usb_ehci *)CONFIG_SYS_FSL_USB_ADDR;
 	hccr = (struct ehci_hccr *)((uint32_t)&ehci->caplength);