exfat: Fix bitwise operation having different size

exfat: Fix bitwise operation having different size

cpos has type loff_t (long long), while s_blocksize has type u32. The
inversion wil happen on u32, the coercion to s64 happens afterwards and
will do 0-left-paddding, resulting in the upper bits getting masked out.

Cast s_blocksize to loff_t before negating it.

Found by static code analysis using Klocwork.

Signed-off-by: Philipp Hahn <phahn-oss@avm.de>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>