ARM: at91/dt: fix typo in sama5d2 pinmux descriptions

PIN_PA15 macro has the same value as PIN_PA14 so we were overriding PA14
mux/configuration.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Reported-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Fixes: 7f16cb67 ("ARM: at91/dt: add sama5d2 pinmux")
Cc: <stable@vger.kernel.org> # v4.4+
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Olof Johansson <olof@lixom.net>