USB: gadget: android: Fix checkpatch related errors

Fix checkpatch error by using snprintf() instead of sprintf().
Also fix checkpatch error by using struct midi_alsa_config *config
instead of struct midi_alsa_config* config.

Change-Id: I093a90971de0a5482a80bc0e5206ac325f11bc92
Signed-off-by: Mayank Rana <mrana@codeaurora.org>