fix param: need to use fsync() and not px4_fsync()

It's used with real OS FD's.

src/modules/systemlib/bson/tinybson.c

@@ -46,7 +46,7 @@
 #include "tinybson.h"
 
 #if 0
-# define debug(fmt, args...)		do { warnx("BSON: " fmt, ##args); } while(0)
+# define debug(fmt, args...)		do { PX4_INFO("BSON: " fmt, ##args); } while(0)
 #else
 # define debug(fmt, args...)		do { } while(0)
 #endif
@@ -56,7 +56,7 @@
 
 #define BSON_READ  read
 #define BSON_WRITE write
-#define BSON_FSYNC px4_fsync
+#define BSON_FSYNC fsync
 
 static int
 read_x(bson_decoder_t decoder, void *p, size_t s)

src/modules/systemlib/param/param.c

@@ -1140,14 +1140,14 @@ param_export(int fd, bool only_unsaved)
 out:
 
 	if (result == 0) {
-		result = bson_encoder_fini(&encoder); // this will call fsync
+		result = bson_encoder_fini(&encoder);
 
 		// write and finish
 		if ((result != 0) || write(fd, encoder.buf, encoder.bufpos) != encoder.bufpos) {
 			PX4_ERR("param write error");
 
 		} else {
-			px4_fsync(fd);
+			fsync(fd);
 		}
 	}