ALSA: ump: Transmit RPN/NRPN message at each MSB/LSB data reception

The UMP 1.1 spec says that an RPN/NRPN should be sent when one of the
following occurs:
* a CC 38 is received
* a subsequent CC 6 is received
* a CC 98, 99, 100, and 101 is received, indicating the last RPN/NRPN
  message has ended and a new one has started

That said, we should send a partial data even if it's not fully
filled.  Let's change the UMP conversion helper code to follow that
rule.

Link: https://patch.msgid.link/20240731130528.12600-2-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>