anv: Handle errors properly in anv_i915_query

anv: Handle errors properly in anv_i915_query

DRM_IOCTL_I915_QUERY is a multi-query.  The most egregious errors are
returned via the usual ioctl error mechanism but there are also
per-query errors that are indicated by item.length < 0.  We need to
handle those as well.  While we're at it, scrape errno so we can return
a proper integer error.

Fixes: c0d07c838a9f "anv: Support i915 query (DRM_IOCTL_I915_QUERY)..."
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11770>