char: select fw_loader by moxa

Select FW_LOADER since moxa needs it, otherwise we face link problems such
as:

drivers/built-in.o: In function
moxa_pci_probe':moxa.c:(.devinit.text+0x76d8): undefined reference to
request_firmware'
:moxa.c:(.devinit.text+0x7e6e): undefined reference to release_firmware'
make: *** [.tmp_vmlinux1] Error 1

Reported-by: Philippe Roussel <p.o.roussel@free.fr>
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>