wl1251: reduce eeprom read wait time

4sec wait is way too pessimistic, TI driver uses 40ms here,
and testing shows that is ebough, so let's also use that.
While at it, add useful sounding comment from the TI driver.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Acked-by: Kalle Valo <kalle.valo@iki.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>