pinctrl: a3700: Fix the issue that gpio controller is registered with wrong node id

In armada_37xx_gpiochip_register, the return value of fdtdec_get_bool
should be true when gpio-controller is found; current codes makes a
wrong inverse return value judgement, this patch fixes it.

Signed-off-by: Ken Ma <make@marvell.com>
Cc: Stefan Roese <sr@denx.de>
Cc: Kostya Porotchkin <kostap@marvell.com>
Cc: Gregory CLEMENT <gregory.clement@free-electrons.com>
Cc: Nadav Haklai <nadavh@marvell.com>
Cc: Wilson Ding <dingwei@marvell.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Stefan Roese <sr@denx.de>