drm/etnaviv: Fix error path on failure to enable bus clk

drm/etnaviv: Fix error path on failure to enable bus clk

[ Upstream commit f8794feaf65cdc97767604cf864775d20b97f397 ]

Since commit 65f037e8e908 ("drm/etnaviv: add support for slave interface
clock") the reg clock is enabled before the bus clock and we need to undo
its enablement on error.

Fixes: 65f037e8e908 ("drm/etnaviv: add support for slave interface clock")
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>