drivers: libata-core: Use usleep_range() instead of msleep() for short sleeps (<20 ms)
Since msleep() may sleep longer than intended time for values less
than 20ms, this patch allows the use of usleep_range for waits less
that 20ms. usleep_range is a finer precision implementation of
msleep and is designed to be a drop-in replacement for udelay
where a precise sleep/busy-wait is unnecessary.
More details can be found at http://lkml.org/lkml/2007/8/3/250
and in Documentation/timers/timers-howto.txt.
This change has been done to improve the performace in PIO6 mode
which is used by viking flash.