drm/edid: In connector_bad_edid() cap num_of_ext by num_blocks read

In commit e11f5bd8 ("drm: Add support for DP 1.4 Compliance edid
corruption test") the function connector_bad_edid() started assuming
that the memory for the EDID passed to it was big enough to hold
`edid[0x7e] + 1` blocks of data (1 extra for the base block). It
completely ignored the fact that the function was passed `num_blocks`
which indicated how much memory had been allocated for the EDID.

Let's fix this by adding a bounds check.

This is important for handling the case where there's an error in the
first block of the EDID. In that case we will call
connector_bad_edid() without having re-allocated memory based on
`edid[0x7e]`.

Fixes: e11f5bd8

 ("drm: Add support for DP 1.4 Compliance edid corruption test")
Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211005192905.v2.1.Ib059f9c23c2611cb5a9d760e7d0a700c1295928d@changeid


Signed-off-by: Dave Airlie <airlied@redhat.com>