tree-wide: when %m is used in log_*, always specify errno explicitly

All those uses were correct, but I think it's better to be explicit.
Using implicit errno is too error prone, and with this change we can require
(in the sense of a style guideline) that the code is always specified.

Helpful query: git grep -n -P 'log_[^s][a-z]+\(.*%m'

src/libsystemd/sd-device/device-enumerator.c

@@ -631,10 +631,8 @@ static int enumerator_scan_devices_tag(sd_device_enumerator *enumerator, const c
         if (!dir) {
                 if (errno == ENOENT)
                         return 0;
-                else {
-                        log_error("sd-device-enumerator: could not open tags directory %s: %m", path);
-                        return -errno;
-                }
+                else
+                        return log_error_errno(errno, "sd-device-enumerator: could not open tags directory %s: %m", path);
         }
 
         /* TODO: filter away subsystems? */
@@ -758,10 +756,8 @@ static int parent_crawl_children(sd_device_enumerator *enumerator, const char *p
         int r = 0;
 
         dir = opendir(path);
-        if (!dir) {
-                log_debug("sd-device-enumerate: could not open parent directory %s: %m", path);
-                return -errno;
-        }
+        if (!dir)
+                return log_debug_errno(errno, "sd-device-enumerate: could not open parent directory %s: %m", path);
 
         FOREACH_DIRENT_ALL(dent, dir, return -errno) {
                 _cleanup_free_ char *child = NULL;

src/libsystemd/sd-device/sd-device.c

@@ -195,8 +195,7 @@ int device_set_syspath(sd_device *device, const char *_syspath, bool verify) {
                                         /* this is not a valid device */
                                         return -ENODEV;
 
-                                log_debug("sd-device: %s does not have an uevent file: %m", syspath);
-                                return -errno;
+                                return log_debug_errno(errno, "sd-device: %s does not have an uevent file: %m", syspath);
                         }
                 } else {
                         /* everything else just needs to be a directory */