riscom8: Auto-load riscom8 module when device opened.

The riscom8 module is missing the char-major-48-* alias that would cause
it to be auto-loaded when a device of that type is opened.  This patch
adds the alias.

Signed-off-by: Scott James Remnant <scott@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>