frontends/omx: fix build warning

From code path, it's easy to see that the variable is only used
with condition, and the variable gets initialized with the same
condition before getting used, but we can initialize it when defined
to avoid the warning.

Signed-off-by: Leo Liu <leo.liu@amd.com>
Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8404>
1 file changed