fs/ntfs3: Remove unnecessary condition checking from ntfs_file_read_iter

This check will be also performed in generic_file_read_iter() so we do
not want to check this two times in a row.

This was founded with Smatch
	fs/ntfs3/file.c:803 ntfs_file_read_iter()
	warn: unused return: count = iov_iter_count()

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