perf test: Fix nanosleep check in the ftrace test

perf test: Fix nanosleep check in the ftrace test

The perf ftrace test case runs:

  perf ftrace profile --graph-opts depth=5 sleep 0.1

and checks that the output contains a *clock_nanosleep function with a
count of 1.

This fails on a risc-v system that uses musl as its C library. musl's
nanosleep syscall wrapper uses either the nanosleep or the
clock_nanosleep syscall.

Filter for sys_*nanosleep to allow both syscalls.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>