serialize: modernize deserialize_{usec|dual_timestamp}() a bit

Rename the return parameters "ret", and use compound initialization. Add
an assert() on input.

src/shared/serialize.c

@@ -320,6 +320,7 @@ int deserialize_usec(const char *value, usec_t *ret) {
         int r;
 
         assert(value);
+        assert(ret);
 
         r = safe_atou64(value, ret);
         if (r < 0)
@@ -328,12 +329,12 @@ int deserialize_usec(const char *value, usec_t *ret) {
         return 0;
 }
 
-int deserialize_dual_timestamp(const char *value, dual_timestamp *t) {
+int deserialize_dual_timestamp(const char *value, dual_timestamp *ret) {
         uint64_t a, b;
         int r, pos;
 
         assert(value);
-        assert(t);
+        assert(ret);
 
         pos = strspn(value, WHITESPACE);
         if (value[pos] == '-')
@@ -353,8 +354,10 @@ int deserialize_dual_timestamp(const char *value, dual_timestamp *t) {
                 /* trailing garbage */
                 return -EINVAL;
 
-        t->realtime = a;
-        t->monotonic = b;
+        *ret = (dual_timestamp) {
+                .realtime = a,
+                .monotonic = b,
+        };
 
         return 0;
 }

src/shared/serialize.h

@@ -38,8 +38,8 @@ static inline int serialize_item_tristate(FILE *f, const char *key, int value) {
 int deserialize_read_line(FILE *f, char **ret);
 
 int deserialize_fd(FDSet *fds, const char *value);
-int deserialize_usec(const char *value, usec_t *timestamp);
-int deserialize_dual_timestamp(const char *value, dual_timestamp *t);
+int deserialize_usec(const char *value, usec_t *ret);
+int deserialize_dual_timestamp(const char *value, dual_timestamp *ret);
 int deserialize_environment(const char *value, char ***environment);
 int deserialize_strv(char ***l, const char *value);
 int deserialize_pidref(FDSet *fds, const char *value, PidRef *ret);