When number of CPUs utilized by guest Windows is less than defined in
QEMU (i.e., desktop versions of Windows severely limits number of CPU
sockets), patch_and_save_context routine accesses non-existent PRCB and
fails. So, limit number of processed PRCBs by NumberProcessors taken
from guest Windows driver.

Signed-off-by: Viktor Prutyanov <viktor.prutyanov@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20221019235948.656411-1-viktor.prutyanov@redhat.com>