exfat: fix name_hash computation on big endian systems

On-disk format for name_hash field is LE, so it must be explicitly
transformed on BE system for proper result.

Fixes: 370e812b ("exfat: add nls operations")
Cc: stable@vger.kernel.org # v5.7
Signed-off-by: Chen Minqiang <ptpt52@gmail.com>
Signed-off-by: Ilya Ponetayev <i.ponetaev@ndmsystems.com>
Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>