vfio/pci: Fix sizing of DPA and THP express capabilities

When sizing the TPH capability we store the register containing the
table size into the 'dword' variable, but then use the uninitialized
'byte' variable to analyze the size.  The table size is also actually
reported as an N-1 value, so correct sizing to account for this.

The round_up() for both TPH and DPA is unnecessary, remove it.

Detected by Coverity: CID 714665 & 715156

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>