drm/amd/display: Fix p-state allow debug index on dcn31

[Why]
It changed since dcn30 but the hubbub31 constructor hasn't been
modified to reflect this.

[How]
Update the value in the constructor to 0x6 so we're checking the right
bits for p-state allow.

It worked before by accident, but can falsely assert 0 depending on HW
state transitions. The most frequent of which appears to be when
all pipes turn off during IGT tests.

Cc: Harry Wentland <harry.wentland@amd.com>

Fixes: e7031d82 ("drm/amd/display: Add pstate verification and recovery for DCN31")
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Eric Yang <Eric.Yang2@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn31/dcn31_hubbub.c

@@ -1042,5 +1042,7 @@ void hubbub31_construct(struct dcn20_hubbub *hubbub31,
 	hubbub31->detile_buf_size = det_size_kb * 1024;
 	hubbub31->pixel_chunk_size = pixel_chunk_size_kb * 1024;
 	hubbub31->crb_size_segs = config_return_buffer_size_kb / DCN31_CRB_SEGMENT_SIZE_KB;
+
+	hubbub31->debug_test_index_pstate = 0x6;
 }