drm/i915/dp_tunnel: Fix error handling when clearing stream BW in atomic state

drm/i915/dp_tunnel: Fix error handling when clearing stream BW in atomic state

Clearing the DP tunnel stream BW in the atomic state involves getting
the tunnel group state, which can fail. Handle the error accordingly.

This fixes at least one issue where drm_dp_tunnel_atomic_set_stream_bw()
failed to get the tunnel group state returning -EDEADLK, which wasn't
handled. This lead to the ctx->contended warn later in modeset_lock()
while taking a WW mutex for another object in the same atomic state, and
thus within the same already contended WW context.

Moving intel_crtc_state_alloc() later would avoid freeing saved_state on
the error path; this stable patch leaves that simplification for a
follow-up.

Cc: Uma Shankar <uma.shankar@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: <stable@vger.kernel.org> # v6.9+
Fixes: a4efae87ecb2 ("drm/i915/dp: Compute DP tunnel BW during encoder state computation")
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/7617
Reviewed-by: Michał Grzelak <michal.grzelak@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20260320092900.13210-1-imre.deak@intel.com