selftests/bpf: Define SYS_NANOSLEEP_KPROBE_NAME for riscv

Add missing sys_nanosleep name for RISC-V, which is used by some tests
(e.g. attach_probe).

Fixes: 08d0ce30 ("riscv: Implement syscall wrappers")
Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Link: https://lore.kernel.org/bpf/20231004110905.49024-4-bjorn@kernel.org

tools/testing/selftests/bpf/test_progs.h

@@ -417,6 +417,8 @@ int get_bpf_max_tramp_links(void);
 #define SYS_NANOSLEEP_KPROBE_NAME "__s390x_sys_nanosleep"
 #elif defined(__aarch64__)
 #define SYS_NANOSLEEP_KPROBE_NAME "__arm64_sys_nanosleep"
+#elif defined(__riscv)
+#define SYS_NANOSLEEP_KPROBE_NAME "__riscv_sys_nanosleep"
 #else
 #define SYS_NANOSLEEP_KPROBE_NAME "sys_nanosleep"
 #endif