drm/vc4: v3d: simplify clock retrieval

Common pattern of handling deferred probe can be simplified with
dev_err_probe() and devm_clk_get_optional(). This results in much
less code.

Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Reviewed-by: Maíra Canal <mcanal@igalia.com>
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240821214052.6800-6-wahrenst@gmx.net