wl1271: Fix msleep() delay while waiting for completion

After last transmission, the device goes to sleep earlier
than the configured dynamic power save timeout. If timeout
is set to 400ms, device enters into sleep mode at around
330ms since from last TX.

This patch removes the msleep(1), which causes the delay
after ELP wakeup. Replaced with udelay(10), the variation
is around 7-10ms.

Signed-off-by: Saravanan Dhanabal <ext-saravanan.dhanabal@nokia.com>
Reviewed-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>