sndioctl: Flush stdout before polling

If stdout is not flushed, output is not seen by programs using
sndioctl through a pipe (ex. "sndioctl -m | cat" displays nothing).

Patch from Érico Nogueira <ericonr@disroot.org>, idea
from Duncan Overbruck <mail@duncano.de>

sndioctl/sndioctl.c

@@ -1015,6 +1015,7 @@ main(int argc, char **argv)
 			exit(1);
 		}
 		for (;;) {
+                       fflush(stdout);
 			nfds = sioctl_pollfd(hdl, pfds, POLLIN);
 			if (nfds == 0)
 				break;