vdpa/ifc: fix build with GCC 12

vdpa/ifc: fix build with GCC 12

GCC 12 raises the following warning:

../drivers/vdpa/ifc/ifcvf_vdpa.c: In function ‘vdpa_enable_vfio_intr’:
../drivers/vdpa/ifc/ifcvf_vdpa.c:383:62: error: writing 4 bytes into a
    region of size 0 [-Werror=stringop-overflow=]
  383 |                         fd_ptr[RTE_INTR_VEC_RXTX_OFFSET + i] = fd;
      |                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
../drivers/vdpa/ifc/ifcvf_vdpa.c:348:14: note: at offset 32 into
    destination object ‘irq_set_buf’ of size 32
  348 |         char irq_set_buf[MSIX_IRQ_SET_BUF_LEN];
      |              ^~~~~~~~~~~

Validate number of vrings to avoid out of bound access.

Bugzilla ID: 855
Cc: stable@dpdk.org
Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Xiao Wang <xiao.w.wang@intel.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>