hw/net/rocker: Avoid undefined shifts with more than 31 ports

hw/net/rocker: Avoid undefined shifts with more than 31 ports

In rocker_port_phys_link_status() and rocker_port_phys_enable_read()
we construct a 64-bit value with one bit per front-panel port.
However we accidentally do the shift as 32-bit arithmetic, which
means that if there are more than 31 front-panel ports this is
undefined behaviour.

Fix the problem by ensuring we use 64-bit arithmetic for the whole
calculation. (We won't ever shift off the 64-bit value because
ROCKER_FP_PORTS_MAX is 62.)

Resolves: Coverity CID 1487121, 1487160
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>