[PATCH] Char: mxser_new, clean request_irq call

We always set ASYNC_SHARE_IRQ, so do not test against this flag and request
shared irq directly.  Also remove nonsense comment.

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>