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 <[e-mail]>
Acked-by: Josef Bacik <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/ioctl.c

···
 	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);
 
···
 	return ret;
 }
 EXPORT_SYMBOL(generic_block_fiemap);
+
+#endif  /*  CONFIG_BLOCK  */
 
 static int file_ioctl(struct file *filp, unsigned int cmd,
 		unsigned long arg)