testsuite: Adjust pr96789.c by disabling loop vect

testsuite: Adjust pr96789.c by disabling loop vect

New test gcc.dg/tree-ssa/pr96789.c fails on
arm-none-linux-gnueabihf since loop vectorizer is able to optimize
the two loops which operate on array tmp with load_lanes feature
support, it make dse3 fail to find expected inputs.

As Richard suggested, this patch is to replace option
-ftree-vectorize to -ftree-slp-vectorize -fno-tree-loop-vectorize.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/pr96789.c: Adjusted by disabling loop
	vectorization.