Input: hiddev - fix off-by-one for num_values in uref_multi requests

Found this when working with a HAPP UGCI device. It has a usage with 7
indexes. I could read them all one at a time, but using a multiref it
would only allow me to read the first 6. The patch below fixed it.

Signed-off-by: Ben Collins <bcollins@ubuntu.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>