The recent change (commit 08422d2c: "ALSA: memalloc: Allow NULL
device for SNDRV_DMA_TYPE_CONTINUOUS type") made the PCM preallocation
helper accepting NULL as the device pointer for the default usage.
Drop the snd_dma_continuous_data() usage that became superfluous from
the callers.

Link: https://lore.kernel.org/r/20191105151856.10785-5-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>