exec: Make the MemOp enum cast explicit

Make the MemOp enum cast explicit to use the QEMU
headers with a C++ compiler.

Signed-off-by: Roman Kiryanov <rkir@google.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240618224528.878425-1-rkir@google.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

include/exec/memop.h

@@ -161,7 +161,7 @@ static inline MemOp size_memop(unsigned size)
     /* Power of 2 up to 8.  */
     assert((size & (size - 1)) == 0 && size >= 1 && size <= 8);
 #endif
-    return ctz32(size);
+    return (MemOp)ctz32(size);
 }
 
 /* Big endianness from MemOp.  */