mwifiex: pcie: compatible with wifi-only image while extract wifi-part fw

Sometimes, we might using wifi-only firmware with a combo firmware name,
in this case, do not need to filter bluetooth part from header.

Signed-off-by: Xinming Hu <huxm@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>