Char: synclink, remove unnecessary checks

Stanse found a potential null dereference in mgsl_put_char and
mgsl_write. There is a check for tty being NULL, but it is
dereferenced earlier.

Actually, tty cannot be NULL in .write and .put_char, so remove
the tests.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>