Drivers: hv: vmbus: Replace cpumask_test_cpu(, cpu_online_mask) with cpu_online()

A slight improvement in readability, and this does also remove one
memory access when NR_CPUS == 1!  ;-)

Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Link: https://lore.kernel.org/r/20200617164642.37393-4-parri.andrea@gmail.com


Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>