ARM: dts: sun8i: r40: Use tcon top clock index macros

tcon_tv0, tcon_tv1 nodes have a clock names of tcon-ch0,
tcon-ch1 which are referring tcon_top clocks via index
numbers like 0, 1 with CLK_TCON_TV0 and CLK_TCON_TV1
respectively.

Use the macro in place of index numbers, for more code
readability.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>