btrfs: fix PAGE_SIZE format specifier in open_ctree()

There is an instance of -Wformat when targeting 32-bit architectures due
to using a 'size_t' specifier (which is 'unsigned int' for 32-bit
platforms) to print PAGE_SIZE:

  In file included from fs/btrfs/compression.h:17,
                   from fs/btrfs/extent_io.h:15,
                   from fs/btrfs/locking.h:13,
                   from fs/btrfs/ctree.h:19,
                   from fs/btrfs/disk-io.c:22:
  fs/btrfs/disk-io.c: In function 'open_ctree':
  include/linux/kern_levels.h:5:25: error: format '%zu' expects argument of type 'size_t', but argument 4 has type 'long unsigned int' [-Werror=format=]
  ...
  fs/btrfs/disk-io.c:3398:17: note: in expansion of macro 'btrfs_warn'
   3398 |                 btrfs_warn(fs_info,
        |                 ^~~~~~~~~~

PAGE_SIZE is consistently defined as an 'unsigned long' in
include/vsdo/page.h so use '%lu' to clear up the warning.

Fixes: 98077f7 ("btrfs: enable experimental bs > ps support")
Reviewed-by: Qu Wenruo <wqu@suse.com>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: nathanchance

fs/btrfs/disk-io.c

@@ -3396,7 +3396,7 @@ int __cold open_ctree(struct super_block *sb, struct btrfs_fs_devices *fs_device
 
 	if (fs_info->sectorsize > PAGE_SIZE)
 		btrfs_warn(fs_info,
-			   "support for block size %u with page size %zu is experimental, some features may be missing",
+			   "support for block size %u with page size %lu is experimental, some features may be missing",
 			   fs_info->sectorsize, PAGE_SIZE);
 	/*
 	 * Handle the space caching options appropriately now that we have the