usb: fix build error without CONFIG_USB_PHY

on i386:

drivers/built-in.o: In function `ci_hdrc_probe':
core.c:(.text+0x20446b): undefined reference to `of_usb_get_phy_mode'

Change-Id: I099a940b2d553abca234eeabe08a8b3b1d5d5298
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Acked-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Git-commit: 848d5b9121e52f63847bf9e156f836db001f51c7
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>