clk: meson: g12a: fix missing uart2 in regmap table

UART2 peripheral is missing from the regmap fixup table of the g12a family
clock controller. As it is, any access to this clock would Oops, which is
not great.

Add the clock to the table to fix the problem.

Fixes: 085a4ea9 ("clk: meson: g12a: add peripheral clock controller")
Reported-by: Dmitry Shmidt <dimitrysh@google.com>
Tested-by: Dmitry Shmidt <dimitrysh@google.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>