mfd: 88pm805: msleep(1ms ~ 20ms) may not do what the caller intends

This code has been working since 2012, as limiting the time between
1ms and 3ms is unlikely to do any harm.

Soothes checkpatch warning:

  WARNING: msleep < 20ms can sleep for up to 20ms;
      see Documentation/timers/timers-howto.txt
  #161: FILE: drivers/mfd/88pm805.c:161:
  +	msleep(1);

Signed-off-by: Lee Jones <lee.jones@linaro.org>