libgfs2: Set errno in dirent_alloc and use dir_add consistently
----- Original Message -----
| Initially spotted by coverity: "error" is passed to a parameter that
| cannot be negative.
| It turned out that dirent_alloc was returning -ENOSPC and some
| code (via dir_add) was assuming that errno was set. Other code was
| assuming that dir_add returned -errno. This patch changes
| to set errno and return -1 and also updates the code which calls
| to use errno.
| Signed-off-by: Andrew Price <firstname.lastname@example.org>