Description: drm/edid: Fix a missing-check bug in drm_load_edid_firmware()
References:
 https://cgit.freedesktop.org/drm/drm-misc/commit/?id=9f1f1a2dab38d4ce87a13565cf4dc1b73bef3a5f
 https://lkml.org/lkml/2019/5/24/843
Notes:
 bwh> Root can set a long string and maybe (but probably not) cause a
 bwh> null pointer dereference.  No security impact.
Bugs:
upstream: N/A "Invalid issue"
4.19-upstream-stable: N/A "Invalid issue"
4.9-upstream-stable: N/A "Invalid issue"
3.16-upstream-stable: N/A "Invalid issue"
sid: N/A "Invalid issue"
4.9-stretch-security: N/A "Invalid issue"
3.16-jessie-security: N/A "Invalid issue"