ALSA: emu10k1: Stop using iommu_present()

iommu_get_domain_for_dev() is already perfectly happy to return NULL
if the given device has no IOMMU. Drop the unnecessary check in favour
of just handling that condition appropriately.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/9b506b4a4fe8a7f40aa8bad1aafc82426cf3dd92.1649165210.git.robin.murphy@arm.com


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