ramster: Fix compile warnings due to usage of debugfs_create_size_t

We get tons of "note: expected ‘size_t *’ but argument is of type ‘long
int *’" warnings. This fixes it.

Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>