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>