drm/amd/powerplay: fix boolreturn.cocci warnings

drivers/gpu/drm/amd/amdgpu/../powerplay/hwmgr/ppatomctrl.c:475:10-11: WARNING: return of 0/1 in function 'atomctrl_lookup_gpio_pin' with return type bool

 Return statements in functions returning bool should use
 true/false instead of 1/0.
Generated by: scripts/coccinelle/misc/boolreturn.cocci

CC: yanyang1 <young.yang@amd.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>