drm/amd/display: Simplify bool conversion

./drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c:1610:68-73: WARNING: conversion to bool not needed here

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=4025


Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>