Fix a typo in each_file_in_pack_dir_fn()'s declaration

One parameter is called `file_pach`. On the face of it, this looks as if
it was supposed to talk about a `path` instead of a `pach`.

However, looking at the way this callback is called, it gets fed the
`d_name` from a directory entry, which provides just the file name, not
the full path. Therefore, let's fix this by calling the parameter
`file_name` instead.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

packfile.h

@@ -54,7 +54,7 @@ const char *pack_basename(struct packed_git *p);
 struct packed_git *parse_pack_index(unsigned char *sha1, const char *idx_path);
 
 typedef void each_file_in_pack_dir_fn(const char *full_path, size_t full_path_len,
-				      const char *file_pach, void *data);
+				      const char *file_name, void *data);
 void for_each_file_in_pack_dir(const char *objdir,
 			       each_file_in_pack_dir_fn fn,
 			       void *data);