swiotlb: clean up reporting

This removes needless use of '%p', and refactors the printk calls to
use pr_*() helpers instead.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>