Use safer allocation macros

Use of these macros, apart from the benefits mentioned in the commit
that adds the macros, has some other good side effects:

-  Consistency in getting the size of the object from sizeof(type),
   instead of a mix of sizeof(type) sometimes and sizeof(*p) other
   times.

-  More readable code: no casts, and no sizeof(), so also shorter lines
   that we don't need to cut.

-  Consistency in using array allocation calls for allocations of arrays
   of objects, even when the object size is 1.

Cc: Valentin V. Bartenev <vbartenev@gmail.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>

tests/libsubid/04_nss/libsubid_zzz.c

@@ -76,7 +76,7 @@ static uid_t getnamuid(const char *name) {
 }
 
 static int alloc_uid(uid_t **uids, uid_t id) {
-	*uids = malloc(sizeof(uid_t));
+	*uids = MALLOC(uid_t);
 	if (!*uids)
 		return -1;
 	*uids[0] = id;
@@ -121,7 +121,7 @@ enum subid_status shadow_subid_list_owner_ranges(const char *owner, enum subid_t
 		return SUBID_STATUS_SUCCESS;
 	if (id_type == ID_TYPE_UID && strcmp(owner, "group1") == 0)
 		return SUBID_STATUS_SUCCESS;
-	ranges = (struct subid_range *)malloc(sizeof(struct subid_range));
+	ranges = MALLOC(struct subid_range);
 	if (!ranges)
 		return SUBID_STATUS_ERROR;
 	if (strcmp(owner, "user1") == 0 || strcmp(owner, "group1") == 0) {