HID: logitech-hidpp: leaks and NULL dereferences

Shift the allocation down a few lines to avoid a memory leak and also
add a check for allocation failure.

Fixes: 2f31c5252910 ('HID: Introduce hidpp, a module to handle Logitech hid++ devices')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>