static-nodes: don't hardcode path to mkdir

Makefile.am

@@ -4173,6 +4173,7 @@ substitutions = \
        '|DEBUGTTY=$(DEBUGTTY)|' \
        '|KILL=$(KILL)|' \
        '|KMOD=$(KMOD)|' \
+       '|MKDIR_P=$(MKDIR_P)|' \
        '|QUOTAON=$(QUOTAON)|' \
        '|QUOTACHECK=$(QUOTACHECK)|' \
        '|SYSTEM_SYSVINIT_PATH=$(sysvinitdir)|' \

units/kmod-static-nodes.service.in

@@ -12,5 +12,5 @@ Before=sysinit.target systemd-tmpfiles-setup-dev.service
 
 [Service]
 Type=oneshot
-ExecStartPre=/usr/bin/mkdir -p /run/tmpfiles.d
+ExecStartPre=@MKDIR_P@ /run/tmpfiles.d
 ExecStart=@KMOD@ static-nodes --format=tmpfiles --output=/run/tmpfiles.d/kmod.conf