ptxed: fix --stat without --quiet

When printing a block, ptxed modifies the block's ninsn field in order to get
error diagnostics right.

When --stat is used without --quiet, it alway reports zero instructions.

Fix it by updating the statistics before printing a block, so we count the
original number of instructions.

Change-Id: I9c728edd8b103a667cf8b42471c6ead4c863ba0f
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>