wl1251: do quick poll for cmd complete interrupt

Most of commands are complete on second read from status register, so
it's unwise to sleep after first try, as sleep may take much longer than
desired 1ms (which is actually already too much waiting for most commands).
So use udelay() for first several tries, and only sleep if command takes
longer, like wl1271+ driver does. This shortens typical powersave setup
time from 50+ ms to <1 ms.