tree-optimization/118269 - SLP reduction chain and early breaks

When we create the SLP reduction chain epilogue for the PHIs for
the early exit we fail to properly classify the reduction as SLP
reduction chain.  The following fixes the corresponding checks.

	PR tree-optimization/118269
	* tree-vect-loop.cc (vect_create_epilog_for_reduction):
	Use the correct stmt for the REDUC_GROUP_FIRST_ELEMENT lookup.

	* gcc.dg/vect/vect-early-break_131-pr118269.c: New testcase.