fsdax: mark the iomap argument to dax_iomap_sector as const

From: Christoph Hellwig <[email protected]>

[ Upstream commit 7e4f4b2d689d959b03cb07dfbdb97b9696cb1076 ]

---
Fixes:

fs/dax.c: In function 'dax_iomap_iter':
fs/dax.c:1147:44: error: passing argument 1 of 'dax_iomap_sector' discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]

   const sector_t sector = dax_iomap_sector(iomap, pos);
                                            ^~~~~
fs/dax.c:1009:17: note: expected 'struct iomap *' but argument is of type 'const struct iomap *'
   static sector_t dax_iomap_sector(struct iomap *iomap, loff_t pos)
                 ^~~~~~~~~~~~~~~~

The issue was introduced by the cherry-pick of commit 8df4919cb921 ("fsdax: switch dax_iomap_rw to use iomap_iter")

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/fs/dax.c?h=v5.10.246&id=8df4919cb921b28809d05feae3e98dc5d8b48146

The upstream change made callers pass a const struct iomap *:
const struct iomap *iomap = &iomi->iomap;
but dax_iomap_sector() still expected a mutable pointer:
static sector_t dax_iomap_sector(struct iomap *iomap, loff_t pos)

 fs/dax.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 91820b9b50b7..2ca33ef5d519 100644
@@ -1006,7 +1006,7 @@ int dax_writeback_mapping_range(struct address_space *mapping,
 }
 EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
 
-static sector_t dax_iomap_sector(struct iomap *iomap, loff_t pos)
+static sector_t dax_iomap_sector(const struct iomap *iomap, loff_t pos)
 {
 	return (iomap->addr + (pos & PAGE_MASK) - iomap->offset) >> 9;
 }

2.47.3