steamcompmgr: Fix calculated refresh cycle for present timing

The "target FPS" feature divides vblank to achieve a target refresh
rate. Previously, the target frame time was divided by the divisor
again, making it way too small and nonsensical. Correctly calculate
this by multiplying instead of dividing.

Since the real refresh rate may be odd, apply the multiplier after
dividing to avoid rounding error.

src/steamcompmgr.cpp

@@ -7916,11 +7916,10 @@ steamcompmgr_main(int argc, char **argv)
 			int nRealRefresh = g_nNestedRefresh ? g_nNestedRefresh : g_nOutputRefresh;
 			int nTargetFPS = g_nSteamCompMgrTargetFPS ? g_nSteamCompMgrTargetFPS : nRealRefresh;
 			nTargetFPS = std::min<int>( nTargetFPS, nRealRefresh );
-			int nMultiplier = nRealRefresh / nTargetFPS;
+			int nVblankDivisor = nRealRefresh / nTargetFPS;
 
-			int nAppRefresh = nRealRefresh * nMultiplier;
 			g_SteamCompMgrAppRefreshCycle = 1'000'000'000ul / nRealRefresh;
-			g_SteamCompMgrLimitedAppRefreshCycle = 1'000'000'000ul / nAppRefresh;
+			g_SteamCompMgrLimitedAppRefreshCycle = 1'000'000'000ul / nRealRefresh * nVblankDivisor;
 		}
 
 		// Handle presentation-time stuff