statfs: add f_fsid field for third-party code compile

because NuttX doesn't have the device number, so we're not assigning a
valid value here. just memset to zero.

Signed-off-by: zhanghongyu <zhanghongyu@xiaomi.com>

include/sys/statfs.h

@@ -104,6 +104,8 @@
  * Type Definitions
  ****************************************************************************/
 
+typedef struct fsid_s fsid_t;
+
 struct statfs
 {
   uint32_t   f_type;     /* Type of filesystem (see definitions above) */
@@ -114,6 +116,7 @@ struct statfs
   fsblkcnt_t f_bavail;   /* Free blocks avail to non-superuser */
   fsfilcnt_t f_files;    /* Total file nodes in the file system */
   fsfilcnt_t f_ffree;    /* Free file nodes in the file system */
+  fsid_t     f_fsid;     /* Encode device type, not yet in use */
 };
 
 /****************************************************************************

include/sys/types.h

@@ -294,6 +294,11 @@ typedef uint24_t u_int24_t;
 typedef uint64_t u_int64_t;
 #endif
 
+struct fsid_s
+{
+  int val[2];
+};
+
 /* Task entry point */
 
 typedef CODE int (*main_t)(int argc, FAR char *argv[]);