avdevice/oss_audio: Add #if HAVE_UNISTD_H around #include <unistd.h>

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavdevice/oss_audio.c

@@ -30,7 +30,9 @@
 #else
 #include <sys/soundcard.h>
 #endif
+#if HAVE_UNISTD_H
 #include <unistd.h>
+#endif
 #include <fcntl.h>
 #include <sys/ioctl.h>