drm/edid: Clean up errors in drm_edid.c

Fix the following errors reported by checkpatch:

ERROR: do not use assignment in if condition

Signed-off-by: chenxuebing <chenxb_99091@126.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240111063921.8701-1-chenxb_99091@126.com