btrfs: rename variables clashing with global function names

reported by gcc -Wshadow:
page_index, page_offset, new_inode, dev_name

Signed-off-by: David Sterba <dsterba@suse.cz>
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 0ac712e..3e285216 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -739,7 +739,7 @@
  *	  for multiple device setup.  Make sure to keep it in sync.
  */
 static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
-		const char *dev_name, void *data)
+		const char *device_name, void *data)
 {
 	struct block_device *bdev = NULL;
 	struct super_block *s;
@@ -762,7 +762,7 @@
 	if (error)
 		return ERR_PTR(error);
 
-	error = btrfs_scan_one_device(dev_name, mode, fs_type, &fs_devices);
+	error = btrfs_scan_one_device(device_name, mode, fs_type, &fs_devices);
 	if (error)
 		goto error_free_subvol_name;