fs/ntfs3: Remove unused variable cnt in ntfs_security_init()

Clang warns:

fs/ntfs3/fsntfs.c:1874:9: warning: variable 'cnt' set but not used
[-Wunused-but-set-variable]
        size_t cnt, off;
               ^
1 warning generated.

It is indeed unused so remove it.

Fixes: 82cae269 ("fs/ntfs3: Add initialization of super block")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Kari Argillander <kari.argillander@gmail.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>