Currently adv7511_get_modes() bails out early when no EDID could be
retrieved. This leaves the previous EDID in place, which is typically not
the intended behavior and might confuse applications. Instead the EDID
should be cleared when no EDID could be retrieved.

All functions that are called after the EDID check handle the case where
the EDID is NULL just fine and exhibit the expected behavior, so just drop
the check.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20170905121018.11477-1-lars@metafoo.de