nfit_test: when clearing poison, also remove badrange entries

The injected badrange entries can only be cleared from the kernel's
accounting by writing to the affected blocks, so when such a write sends
the clear errror DSM to nfit_test, also clear the ranges from
nfit_test's badrange list. This lets an 'ARS Inject error status' DSM to
return the correct status, omitting the cleared ranges.

Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>