dt-bindings: Remove redundant 'maxItems'

There's no need to specify 'maxItems' with the same value as the number
of entries in 'items'. A meta-schema update will catch future cases.

Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Anson Huang <Anson.Huang@nxp.com>
Cc: linux-clk@vger.kernel.org
Cc: linux-pwm@vger.kernel.org
Cc: linux-usb@vger.kernel.org
Reviewed-by: Stephen Boyd <sboyd@kernel.org> # clk
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>