clk: meson-gxbb: round the vdec dividers to closest

We want the video decoder clocks to always round to closest. While the
muxes are already using CLK_MUX_ROUND_CLOSEST, the corresponding
CLK_DIVIDER_ROUND_CLOSEST was forgotten for the dividers.

Fix this by adding the flag to the two vdec dividers.

Fixes: a565242e ("clk: meson: gxbb: add the video decoder clocks")
Signed-off-by: Maxime Jourdan <mjourdan@baylibre.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lkml.kernel.org/r/20190319102537.2043-1-mjourdan@baylibre.com