drm/tilcdc: fix pixel clock setting warning message

The warning message did not printed the LCD pixel clock rate but the LCD
clock divisor input rate. As a consequence, the required and real pixel
clock rates are now passed to the tilcdc_pclk_diff().

Signed-off-by: Dario Binacchi <dariobin@libero.it>
Reviewed-by: Jyri Sarha <jyri.sarha@iki.fi>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Jyri Sarha <jyri.sarha@iki.fi>
Link: https://patchwork.freedesktop.org/patch/msgid/20210322213337.26667-4-dariobin@libero.it