btrfs-progs: convert: don't print message when fs is not recognized, ext2

Bad magic error means it's not the desired filesystem so the error
message is just noise.

Signed-off-by: David Sterba <dsterba@suse.com>

convert/source-ext2.c

@@ -39,6 +39,7 @@ static int ext2_open_fs(struct btrfs_convert_context *cctx, const char *name)
 
 	ret = ext2fs_open(name, open_flag, 0, 0, unix_io_manager, &ext2_fs);
 	if (ret) {
+		if (ret != EXT2_ET_BAD_MAGIC)
 			fprintf(stderr, "ext2fs_open: %s\n", error_message(ret));
 		return -1;
 	}