drm: display: Fix duplicate field initialization in dcn31

Fix the following coccicheck warning:
drivers/gpu/drm/amd/display/dc/dcn31/dcn31_resource.c:917:56-57:
pstate_enabled: first occurrence line 935, second occurrence line 937

Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>