Char: riscom8, change rc_init_drivers prototype

Let compiler decide if the rc_init_drivers function will be inlined and
mark it as __init, because it's called only from __init function.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>