Fix errors raised by missing-prototypes (#46)

Since commit 0fcb708, the Linux kernel globally enforces function
prototype checks. This mandates that each function must have a
declaration to confirm that both the caller and the callee anticipate
the same argument types. Failing to meet this requirement could lead to
serious bugs caused by mismatched prototypes. Therefore, this commit
requires us to add function prototypes to the header files or to declare
functions as static, ensuring compatibility with these changes.

Author: HotMercury

simplefs.h

@@ -108,12 +108,19 @@ struct simplefs_dir_block {
 
 /* superblock functions */
 int simplefs_fill_super(struct super_block *sb, void *data, int silent);
+void simplefs_kill_sb(struct super_block *sb);
 
 /* inode functions */
 int simplefs_init_inode_cache(void);
 void simplefs_destroy_inode_cache(void);
 struct inode *simplefs_iget(struct super_block *sb, unsigned long ino);
 
+/* dentry function */
+struct dentry *simplefs_mount(struct file_system_type *fs_type,
+                              int flags,
+                              const char *dev_name,
+                              void *data);
+
 /* file functions */
 extern const struct file_operations simplefs_file_ops;
 extern const struct file_operations simplefs_dir_ops;