drm/displayid: Iterate over all DisplayID blocks

This will iterate over all DisplayID blocks found in the buffer.
Previously only the first block was parsed.

https://bugs.freedesktop.org/show_bug.cgi?id=95207



Signed-off-by: Tomas Bzatek <tomas@bzatek.net>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>