iommu: Spelling s/cpmxchg64/cmpxchg64/

Fix misspellings of "cmpxchg64"

Fixes: d286a58b ("iommu: Tidy up io-pgtable dependencies")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/eab156858147249d44463662eb9192202c39ab9f.1678295792.git.geert+renesas@glider.be


Signed-off-by: Joerg Roedel <jroedel@suse.de>