staging: wilc1000: give usleep_range a range

usleep_range() is called in non-atomic context so there is little point
in setting min==max as the jitter of hrtimer is determined by interruptions
anyway. usleep_range can only perform the intended coalescence if some
room for placing the hrtimer is provided. Given the range of milliseconds
the delay will be 2+ anyway - so make it 2-2.5 ms which gives hrtimers
space to optimize without negatively impacting performance.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>