lib/scatterlist: use sg_phys() helper

This shorten the length of code in horizential direction, therefore is
easier to read.

Link: https://lkml.kernel.org/r/20241028182920.1025819-1-sui.jingfeng@linux.dev
Signed-off-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: suijingfeng

lib/scatterlist.c

@@ -474,14 +474,14 @@ int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
 		return -EOPNOTSUPP;
 
 	if (sgt_append->prv) {
-		unsigned long next_pfn = (page_to_phys(sg_page(sgt_append->prv)) +
-			sgt_append->prv->offset + sgt_append->prv->length) / PAGE_SIZE;
+		unsigned long next_pfn;
 
 		if (WARN_ON(offset))
 			return -EINVAL;
 
 		/* Merge contiguous pages into the last SG */
 		prv_len = sgt_append->prv->length;
+		next_pfn = (sg_phys(sgt_append->prv) + prv_len) / PAGE_SIZE;
 		if (page_to_pfn(pages[0]) == next_pfn) {
 			last_pg = pfn_to_page(next_pfn - 1);
 			while (n_pages && pages_are_mergeable(pages[0], last_pg)) {