clk: meson: meson8b: fix meson8b_fclk_div3_div clock name

The names of all fclk divider gate clocks follow the naming schema
"fclk_divN" and the name of all fclk fixed dividers follow the naming
schema "fclk_divN_div".
There's one exception to this rule: meson8b_fclk_div3_div's name is
"fclk_div_div3". It's child clock meson8b_fclk_div3 however references
it as "fclk_div3_div" (following the naming schema explained above).

Fix the naming of the meson8b_fclk_div3_div clock to follow the naming
schema. This also fixes serial console on my Meson8m2 board because
"clk81" uses fclk_div3 as parent. However, since the hierarchy stops at
meson8b_fclk_div3 there's no known parent clock and the rate of "clk81"
and all of it's children (UART clock, SDIO MMC controller clock, ...)
are all 0.

Fixes: 05f81440 ("clk: meson: add fdiv clock gates")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>