This fixes a -Waddress-of-packed-member warning about a possibly
unaligned pointer from GCC 9. The pointer is ultimately passed as a9 when calling convert_label().
char * to iconv(), so no alignment is required in practice
__packed has to be removed from struct exfat_dirent as well to fix an
alignment warning when casting from a struct exfat_dirent pointer to a
struct exfat_de_label pointer.