tty: tty_baudrate: Add missing description for 'tty'

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

drivers/tty/tty_baudrate.c:234: warning: Function parameter or member 'tty' not described in 'tty_encode_baud_rate'

Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Jiri Slaby <[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_baudrate.c

···
 
 /**
  *	tty_encode_baud_rate		-	set baud rate of the tty
+ *	@tty:   terminal device
  *	@ibaud: input baud rate
  *	@obaud: output baud rate
  *