libzfsbootenv: lzbe_set_boot_device(): don't free undefined pointer

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Ahelenia Ziemiańska <[email protected]>
Closes #11993

Author: nabijaczleweli

lib/libzfsbootenv/lzbe_device.c

@@ -88,12 +88,11 @@ lzbe_set_boot_device(const char *pool, lzbe_flags_t flag, const char *device)
 		if (strncmp(device, "zfs:", 4) == 0) {
 			fnvlist_add_string(nv, OS_BOOTONCE, device);
 		} else {
-			descriptor = NULL;
-			if (asprintf(&descriptor, "zfs:%s:", device) > 0)
+			if (asprintf(&descriptor, "zfs:%s:", device) > 0) {
 				fnvlist_add_string(nv, OS_BOOTONCE, descriptor);
-			else
+				free(descriptor);
+			} else
 				rv = ENOMEM;
-			free(descriptor);
 		}
 	}