hw/cxl: Fix a QEMU_BUILD_BUG_ON() in switch statement scope issue.

hw/cxl: Fix a QEMU_BUILD_BUG_ON() in switch statement scope issue.

As _Static_assert is a declaration, it can't follow a label until C23.
Some older versions of GCC trip up on this one.

This check has no obvious purpose so just remove it.

Reported-by: Jeongtae Park <jtp.park@samsung.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Message-Id: <20231023140210.3089-6-Jonathan.Cameron@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>