drm/radeon/kms: fix typo in radeon_compute_pll_gain

Looks like this got copied from the ddx wrong.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: NAlex Deucher <alexdeucher@gmail.com>
Cc: stable@kernel.org
Signed-off-by: NDave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_legacy_crtc.c

@@ -272,7 +272,7 @@ static uint8_t radeon_compute_pll_gain(uint16_t ref_freq, uint16_t ref_div,
 	if (!ref_div)
 		return 1;
 
-	vcoFreq = ((unsigned)ref_freq & fb_div) / ref_div;
+	vcoFreq = ((unsigned)ref_freq * fb_div) / ref_div;
 
 	/*
 	 * This is horribly crude: the VCO frequency range is divided into