tree-wide: some more [static] related fixes

let's add [static] where it was missing so far

Drop [static] on parameters that can be NULL.

Add an assert() around parameters that have [static] and can't be NULL
hence.

Add some "const" where it was forgotten.

src/udev/scsi_id/scsi_serial.c

@@ -400,6 +400,9 @@ static int append_vendor_model(
                 const struct scsi_id_device *dev_scsi,
                 char buf[static VENDOR_LENGTH + MODEL_LENGTH]) {
 
+        assert(dev_scsi);
+        assert(buf);
+
         if (strnlen(dev_scsi->vendor, VENDOR_LENGTH) != VENDOR_LENGTH)
                 return log_debug_errno(SYNTHETIC_ERRNO(EINVAL),
                                        "%s: bad vendor string \"%s\"",

src/udev/udev-event.c

@@ -156,6 +156,7 @@ static int get_subst_type(const char **str, bool strict, FormatSubstitutionType
         assert(str);
         assert(*str);
         assert(ret_type);
+        assert(ret_attr);
 
         if (*p == '$') {
                 p++;

src/udev/udev-rules.c

@@ -1464,6 +1464,8 @@ static int attr_subst_subdir(char attr[static UTIL_PATH_SIZE]) {
         const char *tail;
         size_t len, size;
 
+        assert(attr);
+
         tail = strstr(attr, "/*/");
         if (!tail)
             return 0;