drm/i915: Fix error code in icl_compute_combo_phy_dpll()

This function is supposed to return zero or negative error codes but it
accidentally returns true on failure.

Fixes: 92a02074

 ("drm/i915: Split shared dpll .get_dplls() into compute and get phases")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/YrVcHArNMTGCSy+9@kili
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>