HID: magicmouse: fix race between input_register() and probe()
Since kernel 3.7, it appears that the input registration occured before
the end of magicmouse_setup_input(). This is shown by receiving a lot of
"EV_SYN SYN_REPORT 1" instead of normal "EV_SYN SYN_REPORT 0".
This value means that the output buffer is full, and the user space
is loosing events.
Using .input_configured guarantees that the race is not occuring, and that
the call of "input_set_events_per_packet(input, 60)" is taken into account
by input_register().