tree-optimization/115640 - outer loop vect with inner SLP permute

tree-optimization/115640 - outer loop vect with inner SLP permute

The following fixes wrong-code when using outer loop vectorization
and an inner loop SLP access with permutation.  A wrong adjustment
to the IV increment is then applied on GCN.

	PR tree-optimization/115640
	* tree-vect-stmts.cc (vectorizable_load): With an inner
	loop SLP access to not apply a gap adjustment.