ARM: dts: lpc32xx: add required clocks property to keypad device node

NXP LPC32xx keypad controller requires a clock property to be defined.

The change fixes the driver initialization problem:

  lpc32xx_keys 40050000.key: failed to get clock
  lpc32xx_keys: probe of 40050000.key failed with error -2

Fixes: 93898eb7

 ("arm: dts: lpc32xx: add clock properties to device nodes")
Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>