drm/tve200: Fix smatch warning

The "ret" variable is ambiguously returning something that
could be zero in the tve200_modeset_init() function, assign
it an explicit error return code to make this unambiguous.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220505215019.2332613-1-linus.walleij@linaro.org