In the callback function of asynchronous MIDI port, some local variables
are declared 'unsigned int', while they're assigned to int value of return
from snd_rawmidi_transmit_peek().
This commit fixes the type.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>