soc/rockchip/rk3399: Use 64 bits in multiplication

This multiplication is of the form u64 = u32 * u32. Despite being stored
in a 64 bit variable, the intermediate value is still calculated using
32 bit math, which could possibly overflow. Cast one of the variables to
a u64 to ensure it uses 64 bit math instead to avoid this.

Change-Id: Ib08624812e933fdca5a51150ab36d3be49383326
Signed-off-by: Jacob Garber <jgarber1@ualberta.ca>
Found-by: Coverity CID 1375443
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34524
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/soc/rockchip/rk3399/mipi.c

@@ -305,7 +305,7 @@ static int rk_mipi_dsi_get_lane_bps(struct rk_mipi_dsi *dsi,
 		       dsi->format);
 		return bpp;
 	}
-	pclk = edid->mode.pixel_clock * MSECS_PER_SEC;
+	pclk = (u64)edid->mode.pixel_clock * MSECS_PER_SEC;
 
 	/* take 1 / 0.8, since mbps must bigger than bandwidth of RGB */
 	target_bps = pclk / panel_data->lanes * bpp / 8 * 10;