criu/mount: Fix flags cast and sizeof(sflags)

The "args" parameter in apply_sb_flags() is unsigned long. Therefore also
use unsigned long for the cast.

The "sflags" variable in do_new_mount() is unsigned long. Therefore use
sizeof(sflags) instead of sizeof(int).

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>