test: Update some cases for vect_partial_vectors_usage_1

test: Update some cases for vect_partial_vectors_usage_1

Commit r11-3393 improved the epilogue loop handling of partial
vectors and we won't use partial vectors to vectorize a single
iteration scalar loop any more.

The affected test cases have only one single iteration in their
epilogues, so we shouldn't expect the vectorization with
partial vector there.

Tested with explicit --param=vect-partial-vector-usage=1 and
default enablement.

gcc/testsuite/ChangeLog:

	* gcc.dg/vect/slp-perm-1.c: Adjust for partial vectors.
	* gcc.dg/vect/slp-perm-5.c: Likewise.
	* gcc.dg/vect/slp-perm-6.c: Likewise.
	* gcc.dg/vect/slp-perm-7.c: Likewise.