cw1200: Less function calls in cw1200_load_firmware_cw1200() after error detection

The functions kfree() and release_firmware() were called in a few cases
by the cw1200_load_firmware_cw1200() function during error handling even if
the passed variables contained still a null pointer.

Corresponding implementation details could be improved by adjustments for
jump targets.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>