usb: gadget: tegra-xudc: Avoid GFP_ATOMIC where it is not needed

There is no need to use GFP_ATOMIC here. It is a probe function, no
spinlock is taken.

Reviewed-by: JC Kuo <jckuo@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Felipe Balbi <balbi@kernel.org>