tty: tty_io: Fix some kernel-doc issues

Demote non-conformant headers and supply some missing descriptions.

Fixes the following W=1 kernel build warning(s):

drivers/tty/tty_io.c:218: warning: Function parameter or member 'file' not described in 'tty_free_file'
drivers/tty/tty_io.c:566: warning: Function parameter or member 'exit_session' not described in '__tty_hangup'
drivers/tty/tty_io.c:1077: warning: Function parameter or member 'tty' not described in 'tty_send_xchar'
drivers/tty/tty_io.c:1077: warning: Function parameter or member 'ch' not described in 'tty_send_xchar'
drivers/tty/tty_io.c:1155: warning: Function parameter or member 'file' not described in 'tty_driver_lookup_tty'
drivers/tty/tty_io.c:1508: warning: Function parameter or member 'tty' not described in 'release_tty'
drivers/tty/tty_io.c:1508: warning: Function parameter or member 'idx' not described in 'release_tty'
drivers/tty/tty_io.c:2973: warning: Function parameter or member 'driver' not described in 'alloc_tty_struct'
drivers/tty/tty_io.c:2973: warning: Function parameter or member 'idx' not described in 'alloc_tty_struct'

Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Jiri Slaby <[e-mail]>
Cc: Nick Holloway <[e-mail]>
Cc: -- <[e-mail]>
Cc: Marko Kohtala <[e-mail]>
Cc: Bill Hawes <[e-mail]>
Cc: "C. Scott Ananian" <[e-mail]>
Cc: Russell King <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/tty_io.c

···
 	spin_unlock(&tty->files_lock);
 }
 
-/**
+/*
  * tty_free_file - free file->private_data
  *
  * This shall be used only for fail path handling when tty_add_file was not
···
 /**
  *	__tty_hangup		-	actual handler for hangup events
  *	@tty: tty device
+ *	@exit_session: if non-zero, signal all foreground group processes
  *
  *	This can be called by a "kworker" kernel thread.  That is process
  *	synchronous but doesn't hold any locks, so we need to make sure we
···
 	return tty_write(file, buf, count, ppos);
 }
 
-/**
+/*
  *	tty_send_xchar	-	send priority character
  *
  *	Send a high priority character to the tty even if stopped
···
 /**
  *	tty_driver_lookup_tty() - find an existing tty, if any
  *	@driver: the driver for the tty
+ *	@file:   file object
  *	@idx:	 the minor number
  *
  *	Return the tty, if found. If not found, return NULL or ERR_PTR() if the
···
 
 /**
  *	release_tty		-	release tty structure memory
+ *	@tty: tty device release
+ *	@idx: index of the tty device release
  *
  *	Release both @tty and a possible linked partner (think pty pair),
  *	and decrement the refcount of the backing module.
···
 }
 
 
-/**
+/*
  *	alloc_tty_struct
  *
  *	This subroutine allocates and initializes a tty structure.