fs/ntfs3: Remove a useless shadowing variable

There is already a 'u8 mask' defined at the top of the function.
There is no need to define a new one here.

Remove the useless and shadowing new 'mask' variable.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Kari Argillander <kari.argillander@gmail.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>