drm/ingenic: Fix pixclock rate for 24-bit serial panels

When using a 24-bit panel on a 8-bit serial bus, the pixel clock
requested by the panel has to be multiplied by 3, since the subpixels
are shifted sequentially.

The code (in ingenic_drm_encoder_atomic_check) already computed
crtc_state->adjusted_mode->crtc_clock accordingly, but clk_set_rate()
used crtc_state->adjusted_mode->clock instead.

Fixes: 28ab7d35

 ("drm/ingenic: Properly compute timings when using a 3x8-bit panel")
Cc: stable@vger.kernel.org # v5.10
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Tested-by: H. Nikolaus Schaller <hns@goldelico.com>	# CI20/jz4780 (HDMI) and Alpha400/jz4730 (LCD)
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20210323144008.166248-1-paul@crapouillou.net