mxser_new, kill unneeded memsets

There is no need to re-zero static global variables' memory, hence memsets
doing this are useless.  alloc_tty_struct also zeroes allocated memory:
another candidate for removing.

This fixes also a bug -- global structures are cleaned up after
initialization of some its parts.
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>