raw/ioat: fix initial ring size check

raw/ioat: fix initial ring size check

When running the ioat_rawdev_autotest, the ring size was initially required
to be 0. This prevented the test being run multiple times, as the ring size
is modified to a non-zero value when running the first test.

A global variable is now used to track the expected ring size, and is used
in the initial value check.  This enables the test to be run more than
once.

Fixes: 849470d522ed ("raw/ioat: add configure, start and stop functions")
Cc: stable@dpdk.org
Reported-by: Yinan Wang <yinan.wang@intel.com>
Signed-off-by: Ciara Power <ciara.power@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>