tty-ldisc: make /proc/tty/ldiscs use ldisc_ops instead of ldiscs
The /proc/tty/ldiscs file is totally and utterly un-interested in the
"struct tty_ldisc" structures, and only cares about the underlying ldisc
operations.
So don't make it create a dummy 'struct ldisc' only to get a pointer to
the operations, and then destroy it. Instead, we split up the function
'tty_ldisc_try_get()', and create a 'get_ldops()' helper that just looks
up the ldisc operations based on the ldisc number.
That makes the code simpler to read (smaller and more well-defined
helper functions), and allows the /proc functions to avoid creating that
useless dummy only to immediately free it again.