wl1271: Increase timeout for command event waiting

Incresed the timeout value for command complete event waiting from 100
ms to 750 ms. In some rare cases it can take about 600 ms before
complete event for join command is received. This is most propably
caused by the firmware being busy with scanning related activities.

Signed-off-by: Teemu Paasikivi <ext-teemu.3.paasikivi@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>