wl12xx: Validate FEM index from ini file and FW

commit 2131d3c2 upstream.

Check for out of bound FEM index to prevent reading beyond ini
memory end.

Signed-off-by: Pontus Fuchs <pontus.fuchs@gmail.com>
Reviewed-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>