device-dax: Fix default return code of range_parse()

The return value of range_parse() indicates the size when it is
positive.  The error code should be negative.

Signed-off-by: Shiyang Ruan <ruansy.fnst@cn.fujitsu.com>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Link: https://lore.kernel.org/r/20210126021331.1059933-1-ruansy.fnst@cn.fujitsu.com


Reported-by: Zhang Qilong <zhangqilong3@huawei.com>
Fixes: 8490e2e2 ("device-dax: add a range mapping allocation attribute")
Signed-off-by: Dan Williams <dan.j.williams@intel.com>