VFS: Convert file->f_dentry->d_inode to file_inode()

Convert file->f_dentry->d_inode to file_inode() so as to get layered
filesystems right.

Found with: git grep '[.>]f_dentry'
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/cris/arch-v32/drivers/sync_serial.c

@@ -604,7 +604,7 @@ static ssize_t __sync_serial_read(struct file *file,
 				  struct timespec *ts)
 {
 	unsigned long flags;
-	int dev = MINOR(file->f_dentry->d_inode->i_rdev);
+	int dev = MINOR(file_inode(file)->i_rdev);
 	int avail;
 	struct sync_port *port;
 	unsigned char *start;