drm/rockchip: dsi: Clean up 'usage_mode' when failing to attach

If we fail to attach the first time (especially: EPROBE_DEFER), we fail
to clean up 'usage_mode', and thus will fail to attach on any subsequent
attempts, with "dsi controller already in use".

Re-set to DW_DSI_USAGE_IDLE on attach failure.

This is especially common to hit when enabling asynchronous probe on a
duel-DSI system (such as RK3399 Gru/Scarlet), such that we're more
likely to fail dw_mipi_dsi_rockchip_find_second() the first time.

Fixes: 71f68fe7 ("drm/rockchip: dsi: add ability to work as a phy instead of full dsi")
Cc: <stable@vger.kernel.org>
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20221019170255.1.Ia68dfb27b835d31d22bfe23812baf366ee1c6eac@changeid