usb: musb: da8xx: Don't print phy error on -EPROBE_DEFER

This suppresses printing the error message "failed to get phy" in the
kernel log when the error is -EPROBE_DEFER. This prevents usless noise
in the kernel log.

Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>