Fix gcc.dg/tree-ssa/ssa-dom-thread-7.c for aarch64

So on another machine with a cross I see 17 jumps threaded, so adjusted
like that.

	PR tree-optimization/120003
	* gcc.dg/tree-ssa/ssa-dom-thread-7.c: Adjust aarch64 expected
	thread2 number of threads.

(cherry picked from commit aa6f1df4ec46a20d2292291b192d3331e51b59f8)