Fix syntax error in bpf_get_prandom_u32

Fixes: #398
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

src/cc/export/helpers.h

@@ -123,7 +123,7 @@ static int (*bpf_probe_read)(void *dst, u64 size, void *unsafe_ptr) =
   (void *) BPF_FUNC_probe_read;
 static u64 (*bpf_ktime_get_ns)(void) =
   (void *) BPF_FUNC_ktime_get_ns;
-static u32 (*bpf_get_prandom_u32) =
+static u32 (*bpf_get_prandom_u32)(void) =
   (void *) BPF_FUNC_get_prandom_u32;
 static int (*bpf_trace_printk_)(const char *fmt, u64 fmt_size, ...) =
   (void *) BPF_FUNC_trace_printk;