Upgrade mtools to 3.0.37

This version contains a fix for -Wstring-concatenation error.

Test: presubmit
Bug: 175068488
Change-Id: Id4f2ae49da91a481ab2625fdf17668689b640794
diff --git a/fs.h b/fs.h
index 7708c06..f856be8 100644
--- a/fs.h
+++ b/fs.h
@@ -21,23 +21,16 @@
 #include "stream.h"
 
 
-typedef struct FsPublic_t {
-	Class_t *Class;
-	int refs;
-	Stream_t *Next;
-	Stream_t *Buffer;
-
-	int serialized;
-	unsigned long serial_number;
-	unsigned int cluster_size;
-	unsigned int sector_size;
-} FsPublic_t;
-
 Stream_t *fs_init(char drive, int mode, int *isRop);
 int fat_free(Stream_t *Dir, unsigned int fat);
 int fatFreeWithDir(Stream_t *Dir, struct directory *dir);
 int fat_error(Stream_t *Dir);
-int fat32RootCluster(Stream_t *Dir);
+uint32_t fat32RootCluster(Stream_t *Dir);
 char getDrive(Stream_t *Stream);
 
+typedef struct Fs_t Fs_t;
+bool getSerialized(Fs_t *File);
+unsigned long getSerialNumber(Fs_t *File);
+uint32_t getClusterBytes(Fs_t *File);
+
 #endif