This patch fixes pin assign of cts and rts signal of UART3.

Currently GPIO3_C2 and C3 pins are assigned but TRM says that
GPIO3_C0 and C1 are correct.

Refer:
  RK3399 TRM v1.4 - Table 19-1 UART Interface Description
Signed-off-by: Katsuhiro Suzuki <katsuhiro@katsuster.net>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>