mfd: wm5110: Add delay before releasing reset line

On the wm5110 it is important the reset line is held for slightly longer
to ensure the device starts up well. This patch adds a 5mS delay for
this.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>