ALSA: ump: Don't clear bank selection after sending a program change

The current code clears the bank selection MSB/LSB after sending a
program change, but this can be wrong, as many apps may not send the
full bank selection with both MSB and LSB but sending only one.
Better to keep the previous bank set.

Fixes: 0b5288f5

 ("ALSA: ump: Add legacy raw MIDI support")
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20240529083823.5778-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>