ALSA: seq: ump: Use the common RPN/bank conversion context

The UMP core conversion helper API already defines the context needed
to record the bank and RPN/NRPN values, and we can simply re-use the
same struct instead of re-defining the same content as a different
name.

Link: https://patch.msgid.link/20240731130528.12600-4-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>