atm: he: Fix undefined sequence points.

atm: he: Fix undefined sequence points.

GCC complains in these queue index operations because we
perform operations of the form:

	x = some_operation(++x);

which is undefined.  Replace with:

	x = some_operation(x + 1);

which is well defined and provides the intended operation.

Signed-off-by: David S. Miller <davem@davemloft.net>