binfmt_misc: add missing 'break' statement

A missing 'break' statement in bm_status_write() results in a user program
receiving '3' when doing the following:

  write(fd, "-1", 2);

Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>