btrfs: log error codes during failures when writing super blocks

When writing super blocks, at write_dev_supers(), we log an error message
when we get some error but we don't show which error we got and we have
that information. So enhance the error messages with the error codes.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: fdmanana

fs/btrfs/disk-io.c

@@ -3752,8 +3752,8 @@ static int write_dev_supers(struct btrfs_device *device,
 			continue;
 		} else if (ret < 0) {
 			btrfs_err(device->fs_info,
-				"couldn't get super block location for mirror %d",
-				i);
+			  "couldn't get super block location for mirror %d error %d",
+			  i, ret);
 			atomic_inc(&device->sb_write_errors);
 			continue;
 		}
@@ -3772,8 +3772,8 @@ static int write_dev_supers(struct btrfs_device *device,
 					    GFP_NOFS);
 		if (IS_ERR(folio)) {
 			btrfs_err(device->fs_info,
-			    "couldn't get super block page for bytenr %llu",
-			    bytenr);
+			  "couldn't get super block page for bytenr %llu error %ld",
+			  bytenr, PTR_ERR(folio));
 			atomic_inc(&device->sb_write_errors);
 			continue;
 		}