selftests/bpf: Fix vmlinux test on s390x

Use a syscall macro to access the nanosleep()'s first argument;
currently the code uses gprs[2] instead of orig_gpr2.
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20230128000650.1516334-18-iii@linux.ibm.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/progs/test_vmlinux.c

@@ -42,7 +42,7 @@ int BPF_PROG(handle__raw_tp, struct pt_regs *regs, long id)
 	if (id != __NR_nanosleep)
 		return 0;
 
-	ts = (void *)PT_REGS_PARM1_CORE(regs);
+	ts = (void *)PT_REGS_PARM1_CORE_SYSCALL(regs);
 	if (bpf_probe_read_user(&tv_nsec, sizeof(ts->tv_nsec), &ts->tv_nsec) ||
 	    tv_nsec != MY_TV_NSEC)
 		return 0;
@@ -60,7 +60,7 @@ int BPF_PROG(handle__tp_btf, struct pt_regs *regs, long id)
 	if (id != __NR_nanosleep)
 		return 0;
 
-	ts = (void *)PT_REGS_PARM1_CORE(regs);
+	ts = (void *)PT_REGS_PARM1_CORE_SYSCALL(regs);
 	if (bpf_probe_read_user(&tv_nsec, sizeof(ts->tv_nsec), &ts->tv_nsec) ||
 	    tv_nsec != MY_TV_NSEC)
 		return 0;