amiserial: remove stale comment

The comment about interrupt routines is stale at least since commit
41c28ff1 (kill _INLINE_) from 2006. So remove the obsolete parts and
leave only "here they start...".

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210714091314.8292-3-jslaby@suse.cz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>