usb: ehci-omap: fix compilation warning

Fixes below compilation warning:
drivers/usb/host/ehci-hcd.c:425:
	warning: 'ehci_port_power' defined but not used

Signed-off-by: Ajay Kumar Gupta <ajay.gupta@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>