pds_vdpa: fix up format-truncation complaint

Our friendly kernel test robot has recently been pointing out
some format-truncation issues.  Here's a fix for one of them.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202311040109.RfgJoE7L-lkp@intel.com/


Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Message-Id: <20231110221802.46841-2-shannon.nelson@amd.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>