media: cec: extron-da-hd-4k-plus: don't use -1 as an error code

The logic at get_edid_tag_location() returns either an offset
or an error condition. However, the error condition uses a
non-standard "-1" value. This hits a Coverity bug, as Coverity
assumes that positive values are underflow. While this is a
false positive, returning error codes as -1 is an issue.

So, instead, use -ENOENT to indicate that the tag was not found.

Fixes: 056f2821 ("media: cec: extron-da-hd-4k-plus: add the Extron DA HD 4K Plus CEC driver")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>