clk: wm831x: fix usleep_range with bad range

The delay here is not in atomic context and does not seem critical with
respect to precision, but usleep_range(min,max) with min==max results in
giving the timer subsystem no room to optimize uncritical delays. Fix
this by setting the range to 2000,3000 us.

Fixes: commit f05259a6 ("clk: wm831x: Add initial WM831x clock driver")
Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>