sound: usb-audio: fix uninitialized variable with M-Audio MIDI interfaces

Fix the snd_usbmidi_create_endpoints_midiman() function, which forgot to
set the out_interval member of the endpoint info structure for Midiman/
M-Audio devices.  Since kernel 2.6.24, any non-zero value makes the
driver use interrupt transfers instead of bulk transfers.  With EHCI
controllers, these random interval values result in unbearably large
latencies for output MIDI transfers.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Reported-by: David <devurandom@foobox.com>
Tested-by: David <devurandom@foobox.com>
Cc: <stable@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>