drm/i915/dp_mst: Simplify handling the single-bpp case during state computation

drm/i915/dp_mst: Simplify handling the single-bpp case during state computation

A follow-up change wants to skip invalid bpps in the bpp select loop of
a stream state computation. To allow for that, using the usual
'continue' statement in the loop, change the way the single-bpp range is
handled.

v2: Fix typo in commit message. (Ankit)

Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://lore.kernel.org/r/20250509180340.554867-3-imre.deak@intel.com