drm/amdgpu/gmc: Remove redundant ternary operators

For ternary operators in the form of "a ? false : true", if 'a' itself
returns a boolean result, the ternary operator can be omitted. Remove
redundant ternary operators to clean up the code.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Liao Yuanhong <liaoyuanhong@vivo.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>