provide generic_block_fiemap() only with BLOCK=y

This fixes the following compile error with CONFIG_BLOCK=n caused by
commit 68c9d702bb72f367f3b148963ec6cf5e07ff7f65 ("generic block based
fiemap implementation"):

    CC      fs/ioctl.o
  fs/ioctl.c: In function 'generic_block_fiemap':
  fs/ioctl.c:249: error: storage size of 'tmp' isn't known
  fs/ioctl.c:272: error: invalid application of 'sizeof' to incomplete type 'struct buffer_head'
  fs/ioctl.c:280: error: implicit declaration of function 'buffer_mapped'
  fs/ioctl.c:249: warning: unused variable 'tmp'
  make[2]: *** [fs/ioctl.o] Error 1

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Acked-by: Josef Bacik <jbacik@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ioctl.c

@@ -226,6 +226,8 @@ static int ioctl_fiemap(struct file *filp, unsigned long arg)
 	return error;
 }
 
+#ifdef CONFIG_BLOCK
+
 #define blk_to_logical(inode, blk) (blk << (inode)->i_blkbits)
 #define logical_to_blk(inode, offset) (offset >> (inode)->i_blkbits);
 
@@ -342,6 +344,8 @@ int generic_block_fiemap(struct inode *inode,
 }
 EXPORT_SYMBOL(generic_block_fiemap);
 
+#endif  /*  CONFIG_BLOCK  */
+
 static int file_ioctl(struct file *filp, unsigned int cmd,
 		unsigned long arg)
 {