HID: usbmouse: Avoid GFP_ATOMIC when GFP_KERNEL is possible

probe in usb don't need to be atomic. So GFP_KERNEL can be used here,
instead of GFP_ATOMIC.

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>