Xarray: use xa_mark_t in xas_squash_marks() to keep code consistent

Besides xas_squash_marks(), all functions use xa_mark_t type to iterate
all possible marks.  Use xa_mark_t in xas_squash_marks() to keep code
consistent.

Link: https://lkml.kernel.org/r/20241213122523.12764-6-shikemeng@huaweicloud.com


Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Mattew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>