usb: host: max3421-hcd: unconditionally use GFP_ATOMIC in max3421_urb_enqueue()

As far as kzalloc() is called with spinlock held,
we have to pass GFP_ATOMIC regardless of mem_flags argument.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Acked-by: David Mosberger <davidm@egauge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>