drm/bridge: tc358768: Rename dsibclk to hsbyteclk

The Toshiba documentation talks about HSByteClk when referring to the
DSI HS byte clock, whereas the driver uses 'dsibclk' name. Also, in a
few places the driver calculates the byte clock from the DSI clock, even
if the byte clock is already available in a variable.

To align the driver with the documentation, change the 'dsibclk'
variable to 'hsbyteclk'. This also make it easier to visually separate
'dsibclk' and 'dsiclk' variables.

Reviewed-by: Peter Ujfalusi <peter.ujfalusi@gmail.com>
Tested-by: Maxim Schwalm <maxim.schwalm@gmail.com> # Asus TF700T
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230906-tc358768-v4-9-31725f008a50@ideasonboard.com