staging: lustre: replace MIN/MAX with min_t/max_t

Switch from MIN/MAX to min_t/max_t with a size_t type.  The size_t type
was chosen because one operand is a size_t and all the others are
immediate integer values.

Signed-off-by: Jeremiah Mahler <jmmahler@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>