Fix conflict with unistd.h

Rename pause() to pause_play().

This commit fixes the following build error:

../audio/out/ao_pulse.c:539:13: error: conflicting types for ‘pause’; have ‘void(struct ao *)’
  539 | static void pause(struct ao *ao)
      |             ^~~~~
In file included from /usr/include/bits/sigstksz.h:24,
                 from /usr/include/signal.h:328,
                 from /usr/include/sys/param.h:28,
                 from /usr/include/pulse/sample.h:26,
                 from /usr/include/pulse/def.h:28,
                 from /usr/include/pulse/direction.h:23,
                 from /usr/include/pulse/pulseaudio.h:24,
                 from ../audio/out/ao_pulse.c:28:
/usr/include/unistd.h:489:12: note: previous declaration of ‘pause’ with type ‘int(void)’
  489 | extern int pause (void);
      |            ^~~~~

src/mpv/audio/out/ao_null.c

@@ -139,7 +139,7 @@ static void reset(struct ao *ao)
 }
 
 // stop playing, keep buffers (for pause)
-static void pause(struct ao *ao)
+static void pause_play(struct ao *ao)
 {
     struct priv *priv = ao->priv;
 
@@ -227,7 +227,7 @@ const struct ao_driver audio_out_null = {
     .get_space = get_space,
     .play      = play,
     .get_delay = get_delay,
-    .pause     = pause,
+    .pause     = pause_play,
     .resume    = resume,
     .drain     = wait_drain,
     .priv_size = sizeof(struct priv),

src/mpv/audio/out/ao_pulse.c

@@ -536,7 +536,7 @@ static void reset(struct ao *ao)
 }
 
 // Pause the audio stream by corking it on the server
-static void pause(struct ao *ao)
+static void pause_play(struct ao *ao)
 {
     cork(ao, true);
 }
@@ -810,7 +810,7 @@ const struct ao_driver audio_out_pulse = {
     .get_space = get_space,
     .play      = play,
     .get_delay = get_delay,
-    .pause     = pause,
+    .pause     = pause_play,
     .resume    = resume,
     .drain     = drain,
     .wait      = wait_audio,