Input: uinput - remove BKL from uinput_open function

Commit 87029658

 pushed down the BKL
into uinput open function. However, there's nothing that needs locking
in there.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>