ALSA: bebob: code refactoring for callback function to rawmidi interface

The pairs of rawmidi.hw_params callback functions and .hw_free callback
functions for both direction have no differences.

This commit unifies the pairs.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>