ALSA: seq: Fix missing channel at encoding RPN/NRPN MIDI2 messages

[ Upstream commit c5ab94ea ]

The conversion from the legacy event to MIDI2 UMP for RPN and NRPN
missed the setup of the channel number, resulting in always the
channel 0.  Fix it.

Fixes: e9e02819 ("ALSA: seq: Automatic conversion of UMP events")
Link: https://patch.msgid.link/20240625095200.25745-1-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>