ALSA: ump: Export snd_ump_receive_ump_val()

This is another preliminary patch for USB MIDI 2.0 gadget driver.
Export the currently local snd_ump_receive_ump_val().  It can be used
by the gadget driver for processing the UMP data.

Link: https://lore.kernel.org/r/20230621110241.4751-4-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>