[PATCH] Char: mxser_new, fix sparse warning

Feed NULL instead of 0 where pointer is expected.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: <osv@javad.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>