ASoC: wm_adsp: Use usleep_range for short delay

Replace the 1ms msleep in wm_adsp2_ena with a usleep_range, as per
normal guidance on delay functions. Also tighten up the delay a little
as 1ms was quite generous.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>