HID: sony: remove duplicate NULL check before calling usb_free_urb()

usb_free_urb() does the NULL check itself, so there is no need to duplicate
it prior to calling.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: e1cd4004 ("HID: sony: Fix a potential memory leak in sony_probe()")
Signed-off-by: Jiri Kosina <jkosina@suse.cz>