wireless: mwifiex: remove unreachable paths

We know 'firmware' is non-NULL from the beginning of mwifiex_prog_fw_w_helper,
remove all !firmware paths from the rest of the function.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>