Drivers: hv: vmbus: Fix synic per-cpu context initialization

If hv_synic_alloc() errors out, the state of the per-cpu context
for some CPUs is unknown since the zero'ing is done as each
CPU is iterated over.  In such case, hv_synic_cleanup() may try to
free memory based on uninitialized values.  Fix this by zero'ing
the per-cpu context for all CPUs before doing any memory
allocations that might fail.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>