duplicate htons() in check_file_directory_conflict()

Hi,

create_ce_flags() macro calls htons() so the htons()s in check_file_directory_conflict() should be removed or alternatively htons should be removed from the create_ce_flags macro. I noticed the bug when compiling cogito with -Wshadow.

read-cache.c:208
        pos = cache_name_pos(pathbuf,
                             htons(create_ce_flags(len, stage)));

read-cache.c:232
        pos = cache_name_pos(path,
                             htons(create_ce_flags(namelen, stage)));