fsdax: simplify the offset check in dax_iomap_zero

The file relative offset must have the same alignment as the storage
offset, so use that and get rid of the call to iomap_sector.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/20211129102203.2243509-17-hch@lst.deSigned-off-by: Dan Williams <dan.j.williams@intel.com>

fs/dax.c

@@ -1123,7 +1123,6 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
 
 s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
 {
-	sector_t sector = iomap_sector(iomap, pos & PAGE_MASK);
 	pgoff_t pgoff = dax_iomap_pgoff(iomap, pos);
 	long rc, id;
 	void *kaddr;
@@ -1131,8 +1130,7 @@ s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
 	unsigned offset = offset_in_page(pos);
 	unsigned size = min_t(u64, PAGE_SIZE - offset, length);
 
-	if (IS_ALIGNED(sector << SECTOR_SHIFT, PAGE_SIZE) &&
-	    (size == PAGE_SIZE))
+	if (IS_ALIGNED(pos, PAGE_SIZE) && size == PAGE_SIZE)
 		page_aligned = true;
 
 	id = dax_read_lock();