wl1271: Correct memory handling for FW boot

Several memory allocation related failure cases were not properly
handled by the driver - the result was that in low memory conditions
booting of a corrupted FW could be attempted - and user space would not
get proper failure code.

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