Commit a17d609e ("drm/panfrost: Don't corrupt the queue mutex on
open/close") left unused variables behind, thus generating a warning
at compilation time. Remove those variables.

Fixes: a17d609e ("drm/panfrost: Don't corrupt the queue mutex on open/close")
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201101173817.831769-1-boris.brezillon@collabora.com