llkd: test: llkd.sleep also check for __arm64_sys_openat

4.19 kernel reported __arm64_sys_openat instead of SyS_openat, so
the test for llkd.sleep also needs to check for that as well.

Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 147486902
Test: llkd_unit_test
Change-Id: Ibb4b4ca45391e35fd03fcb8e7ccea01f547b76e1