[ALSA] usb-audio: use vmalloc for the PCM buffer

USB generic driver
With the double buffering, we no longer need contiguous memory for the
PCM buffer, so we can use vmalloc() instead of the preallocation
functions, and increase the maximum size to 256 KB.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
1 file changed