dt-bindings: mvebu-uart: update information about UART clock

dt-bindings: mvebu-uart: update information about UART clock

Device "marvell,armada-3700-uart" should use
"marvell,armada-3700-uart-clock" compatible clock.

Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Marek Behún <kabel@kernel.org>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Marek Behún <kabel@kernel.org>
Link: https://lore.kernel.org/r/20220219152818.4319-5-kabel@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>