libbpf: Fix arm64 build

The macro for libbpf_smp_store_release() doesn't build on arm64, fix it.

Fixes: 291471dd ("libbpf, xsk: Add libbpf_smp_store_release libbpf_smp_load_acquire")
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210308182521.155536-1-jean-philippe@linaro.org

tools/lib/bpf/libbpf_util.h

@@ -35,7 +35,7 @@ extern "C" {
 		typeof(*p) ___p1;					\
 		asm volatile ("ldar %w0, %1"				\
 			      : "=r" (___p1) : "Q" (*p) : "memory");	\
-		__p1;							\
+		___p1;							\
 	})
 #elif defined(__riscv)
 # define libbpf_smp_store_release(p, v)					\