drm/amd/display: Fix context alloc failed logging

Since there was no return statement in the fail block immediately
preceding the context_alloc_fail block, any failure within the
function caused a context alloc failed error message to be printed.
Since the context_alloc_fail block is only used once, move it to
where the goto is directly and accompany it with a return statement.

Signed-off-by: Andrew Jiang <Andrew.Jiang@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>