fs/ntfs3: Initiliaze sb blocksize only in one place + refactor

Right now sb blocksize first get initiliazed in fill_super but in can be
changed in helper function. It makes more sense to that this happened
only in one place.

Because we move this to helper function it makes more sense that
s_maxbytes will also be there. I rather have every sb releted thing in
fill_super, but because there is already sb releted stuff in this
helper. This will have to do for now.

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