pkg-stats: use correct variable names for convert_to_*autotools

The variable convert_to_autotools is not used in the script.  The correct
variables are convert_to_target_autotools and convert_to_host_autotools.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>