am33xx: ignore return value from usb_ether_init()

In 2cb43ef1 ("usb: ether: Fix error handling in usb_ether_init") the error
handling of usb_ether_init() was changed. Not a single other call site of this
function checks its return value, therefore follow suit in the am33xx code.

Do not cause the boot to halt if the usb gadget ethernet initialization fails:

	initcall sequence 9ffdbd84 failed at call 808024b9 (err=-19)
	### ERROR ### Please RESET the board ###

Signed-off-by: Trevor Woerner <twoerner@gmail.com>
Reviewed-by: Michal Suchánek <msuchanek@suse.de>