fs: btrfs: Rename struct btrfs_path to struct __btrfs_path

To avoid name conflicting between the extent buffer based btrfs_path
from btrfs-progs, rename struct btrfs_path to struct __btrfs_path.

Also rename btrfs_free_path() to __btrfs_free_path() to avoid conflicts.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Marek BehĂșn <marek.behun@nic.cz>
diff --git a/fs/btrfs/extent-io.c b/fs/btrfs/extent-io.c
index eec89d1..a524145 100644
--- a/fs/btrfs/extent-io.c
+++ b/fs/btrfs/extent-io.c
@@ -14,7 +14,7 @@
 #include "extent-io.h"
 #include "disk-io.h"
 
-u64 btrfs_read_extent_inline(struct btrfs_path *path,
+u64 btrfs_read_extent_inline(struct __btrfs_path *path,
 			     struct btrfs_file_extent_item *extent, u64 offset,
 			     u64 size, char *out)
 {
@@ -66,7 +66,7 @@
 	return -1ULL;
 }
 
-u64 btrfs_read_extent_reg(struct btrfs_path *path,
+u64 btrfs_read_extent_reg(struct __btrfs_path *path,
 			  struct btrfs_file_extent_item *extent, u64 offset,
 			  u64 size, char *out)
 {