UPSTREAM: usb: of: fix build breakage on !OF

UPSTREAM: usb: of: fix build breakage on !OF

If OF is disabled, we will try to define a stub for
of_usb_get_dr_mode_by_phy(), however that missed a
static inline annotation which made us redefine the
stub over and over again. Fix that.

Change-Id: I0e3594d2beb29273343dacf0af73f159ad30a35d
Fixes: 98bfb3946695 ("usb: of: add an api to get
	dr_mode by the phy node")
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Wu Liang feng <wulf@rock-chips.com>
(cherry picked from commit be99c84300950e876074916b215b511f69f83d3b)