libnvdimm: fix clear length of nvdimm_forget_poison()

libnvdimm: fix clear length of nvdimm_forget_poison()

commit 8d13c0290655b883df9083a2a0af0d782bc38aef upstream.

ND_CMD_CLEAR_ERROR command returns 'clear_err.cleared', the length
of error actually cleared, which may be smaller than its requested
'len'.

Change nvdimm_clear_poison() to call nvdimm_forget_poison() with
'clear_err.cleared' when this value is valid.

Fixes: e046114af5fc ("libnvdimm: clear the internal poison_list when clearing badblocks")
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>