hamradio: Resolve memory leak due to missing firmware release in add_mcs()

Failure to release_firmware() in drivers/net/hamradio/yam.c::add_mcs()
causes memory leak.
This patch should fix it.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: David S. Miller <davem@davemloft.net>