drm/nva3: fix overflow in fixed point math used for pll calculation

	       int *N, int *fN, int *M, int *P)

{

	fixed20_12 fb_div, a, b;

	u32 refclk = pll->refclk / 10;

	u32 max_vco_freq = pll->vco1.maxfreq / 10;

	u32 max_vco_inputfreq = pll->vco1.max_inputfreq / 10;

	clk /= 10;

	*P = pll->vco1.maxfreq / clk;

	*P = max_vco_freq / clk;

	if (*P > pll->max_p)

		*P = pll->max_p;

	if (*P < pll->min_p)

		*P = pll->min_p;

	/* *M = ceil(refclk / pll->vco.max_inputfreq); */

	a.full = dfixed_const(pll->refclk);

	b.full = dfixed_const(pll->vco1.max_inputfreq);

	/* *M = floor((refclk + max_vco_inputfreq) / max_vco_inputfreq); */

	a.full = dfixed_const(refclk + max_vco_inputfreq);

	b.full = dfixed_const(max_vco_inputfreq);

	a.full = dfixed_div(a, b);

	a.full = dfixed_ceil(a);

	a.full = dfixed_floor(a);

	*M = dfixed_trunc(a);

	/* fb_div = (vco * *M) / refclk; */

	fb_div.full = dfixed_const(clk * *P);

	fb_div.full = dfixed_mul(fb_div, a);

	a.full = dfixed_const(pll->refclk);

	a.full = dfixed_const(refclk);

	fb_div.full = dfixed_div(fb_div, a);

	/* *N = floor(fb_div); */