wl1271: Update busyword checking mechanism

After the busy-words, if the firmware did not complete by the end of the
first (fixed) busy-word, a flip of the CS line is required to enable clocking
out the actual read data.

This patch changes the mechanism such that the CS line is flipped after each
busyword.

Also, the busy-word mechanism is finally enabled, and the number of fixed
busywords reduced to the minimum.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Teemu Paasikivi <ext-teemu.3.paasikivi@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>