fs/ntfs3: Remove redundant assignment to variable frame

Variable frame is assigned a value that is never read. The
assignment is redundant and can be removed. Cleans up the
clang-scan build warning:

fs/ntfs3/file.c:995:3: warning: Value stored to 'frame' is
never read [deadcode.DeadStores]
                frame = pos >> frame_bits;

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>