control.h: Fix ump header file detection

Apparently, the control.h is used from apps separately (outside
asoundlib.h). Avoid errors like:

/usr/include/alsa/control.h:417:47: error: ‘snd_ump_endpoint_info_t’ has not been declared
  417 | int snd_ctl_ump_endpoint_info(snd_ctl_t *ctl, snd_ump_endpoint_info_t *info);
      |                                               ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/alsa/control.h:418:44: error: ‘snd_ump_block_info_t’ has not been declared
  418 | int snd_ctl_ump_block_info(snd_ctl_t *ctl, snd_ump_block_info_t *info);
      |                                            ^~~~~~~~~~~~~~~~~~~~

Fixes: #348
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

include/control.h

@@ -413,6 +413,8 @@ int snd_ctl_pcm_prefer_subdevice(snd_ctl_t *ctl, int subdev);
 int snd_ctl_rawmidi_next_device(snd_ctl_t *ctl, int * device);
 int snd_ctl_rawmidi_info(snd_ctl_t *ctl, snd_rawmidi_info_t * info);
 int snd_ctl_rawmidi_prefer_subdevice(snd_ctl_t *ctl, int subdev);
+#endif
+#ifdef __ALSA_UMP_H
 int snd_ctl_ump_next_device(snd_ctl_t *ctl, int *device);
 int snd_ctl_ump_endpoint_info(snd_ctl_t *ctl, snd_ump_endpoint_info_t *info);
 int snd_ctl_ump_block_info(snd_ctl_t *ctl, snd_ump_block_info_t *info);