libmultipath: use asprintf() to allocate prefixed_uuid

gcc 12.0.1 failed building libmultipath due to a format-overflow false
positive on 32-bit architectures.  This isn't so surprising as
format-overflow=2 is very aggressive in the assumptions it makes about
the arguments.  Here, it assumes that mpp->wwid could take up all the
space that a pointer could point to, even if I add code to this function
to explicitly null terminate mpp->wwid to fit in WWID_SIZE.

To avoid this and simplify the function, switch from using calloc() and
sprintf() to just using asprintf().

For reference, the gcc build error that this fixes is:

devmapper.c: In function 'dm_addmap.constprop.0':
devmapper.h:27:21: error: '%s' directive writing up to 2147483644 bytes into a region of size 2147483641 [-Werror=format-overflow=]
   27 | #define UUID_PREFIX "mpath-"
      |                     ^~~~~~~~
devmapper.c:484:53: note: format string is defined here
  484 |                 sprintf(prefixed_uuid, UUID_PREFIX "%s", mpp->wwid);
      |                                                     ^~

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Reviewed-by: Martin Wilck <mwilck@suse.com>

libmultipath/devmapper.c

@@ -473,14 +473,11 @@ dm_addmap (int task, const char *target, struct multipath *mpp,
 		dm_task_set_ro(dmt);
 
 	if (task == DM_DEVICE_CREATE) {
-		prefixed_uuid = calloc(1, UUID_PREFIX_LEN +
-				       strlen(mpp->wwid) + 1);
-		if (!prefixed_uuid) {
+		if (asprintf(&prefixed_uuid, UUID_PREFIX "%s", mpp->wwid) < 0) {
 			condlog(0, "cannot create prefixed uuid : %s",
 				strerror(errno));
 			goto addout;
 		}
-		sprintf(prefixed_uuid, UUID_PREFIX "%s", mpp->wwid);
 		if (!dm_task_set_uuid(dmt, prefixed_uuid))
 			goto freeout;
 		dm_task_skip_lockfs(dmt);