mm/gup_test.c: convert verify_dma_pinned() to us folios

verify_dma_pinned() checks that pages are dma-pinned.  We can convert this
to use folios.

Link: https://lkml.kernel.org/r/20230614021312.34085-4-vishal.moola@gmail.com


Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>