tests: Fix gem5 stdlib NPB example test

'--maxinst' was replaced with '--ticks' for the
'configs/example/gem5_library/x86-npb-benchmarks.py' script. This test
was never updated and resulted in failure. This patch fixes the issue.

Change-Id: I5491d48e3d42c37f703600a3dea323146e5ff6d7
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/56223
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

tests/gem5/gem5_library_example_tests/test_gem5_library_examples.py

@@ -128,7 +128,7 @@ if os.access("/dev/kvm", mode=os.R_OK | os.W_OK):
             "bt",
             "--size",
             "A",
-            "--maxinsts",
+            "--ticks",
             "5000000000"
         ],
         valid_isas=(constants.x86_tag,),