coccinelle: make use of SYNTHETIC_ERRNO

Ideally, coccinelle would strip unnecessary braces too. But I do not see any
option in coccinelle for this, so instead, I edited the patch text using
search&replace to remove the braces. Unfortunately this is not fully automatic,
in particular it didn't deal well with if-else-if-else blocks and ifdefs, so
there is an increased likelikehood be some bugs in such spots.

I also removed part of the patch that coccinelle generated for udev, where we
returns -1 for failure. This should be fixed independently.

src/nspawn/nspawn-cgroup.c

@@ -525,8 +525,8 @@ static int mount_unified_cgroups(const char *dest) {
                 if (errno != ENOENT)
                         return log_error_errno(errno, "Failed to determine if mount point %s contains the unified cgroup hierarchy: %m", p);
 
-                log_error("%s is already mounted but not a unified cgroup hierarchy. Refusing.", p);
-                return -EINVAL;
+                return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
+                                       "%s is already mounted but not a unified cgroup hierarchy. Refusing.", p);
         }
 
         return mount_verbose(LOG_ERR, "cgroup", p, "cgroup2", MS_NOSUID|MS_NOEXEC|MS_NODEV, NULL);