ksmbd: set the range of bytes to zero without extending file size in FSCTL_ZERO_DATA

generic/091, 263 test failed since commit f66f8b94

 ("cifs: when
extending a file with falloc we should make files not-sparse").
FSCTL_ZERO_DATA sets the range of bytes to zero without extending file
size. The VFS_FALLOCATE_FL_KEEP_SIZE flag should be used even on
non-sparse files.

Cc: stable@vger.kernel.org
Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>