X86: Remove double-cast in Cvtf2i micro-op

This double cast led to rounding errors which caused
some benchmarks to get the wrong values, most notably lucas
which failed spectacularly due to CVTTSD2SI returning an
off-by-one value.  equake was also broken.

src/arch/x86/isa/microops/mediaop.isa

@@ -1237,7 +1237,7 @@ let {{
                 }
 
                 if (destSize == 4) {
-                    argBits = (uint32_t)(float)arg;
+                    argBits = (uint32_t)arg;
                 } else {
                     argBits = (uint64_t)arg;
                 }