usb: host: ehci-tegra: request deferred probe when failing to get phy

The commit 1290a958 ("usb: phy: propagate __of_usb_find_phy()'s error on
failure") changed the condition to return -EPROBE_DEFER to host driver.
Originally the Tegra host driver depended on the returned -EPROBE_DEFER to
get the phy device later when booting. Now we have to do that explicitly.

Signed-off-by: Vince Hsu <vinceh@nvidia.com>
Tested-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>