fs/ntfs3: Convert mount options to pointer in sbi

Use pointer to mount options. We want to do this because we will use new
mount api which will benefit that we have spi and mount options in
different allocations. When we remount we do not have to make whole new
spi it is enough that we will allocate just mount options.

Please note that we can do example remount lot cleaner but things will
change in next patch so this should be just functional.

Signed-off-by: Kari Argillander <kari.argillander@gmail.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>