We can't pass error pointers to brelse().

Fixes: fb265c9c ("ext4: add ext4_sb_bread() to disambiguate ENOMEM cases")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NTheodore Ts'o <tytso@mit.edu>
Reviewed-by: NJan Kara <jack@suse.cz>