drm/dp: Fix bogus DPCD version check in drm_dp_read_downstream_info()

Ville pointed this out to me when fixing some issues in
drm_dp_read_downstream_info() - the DPCD version check here is bogus as
there's no DisplayPort versions prior to 1.0. The original code from i915
that this was extracted from actually did:

  dpcd[DP_DPCD_REV] == DP_DPCD_REV_10

Which is correct, and somehow got missed when extracting this function. So
let's fix this. Note that as far as I'm aware, I don't think this fixes any
actual issues users are hitting.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210507214209.554866-1-lyude@redhat.com