shmem: use PRI64 to print u64 (v2)

shmem.c:290:4: note: in expansion of macro 'pr_err'
    pr_err("Shmem %lx already collected as SYSVIPC\n", vi->shmid);
    ^

v2: fix one more place
Signed-off-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>