Add explicit support for splicing from pipe to file through
iter_file_splice_write(). Commit 
36e2c7421f02 ("fs: don't allow splice
read/write without explicit ops") removed the default .splice_write
operation which effectively removed UDF support for splicing from pipe.
Fixes: 36e2c7421f02 ("fs: don't allow splice read/write without explicit ops")
Reported-by: kernel test robot <yujie.liu@intel.com>
Link: https://lore.kernel.org/r/202209081443.593ab12-yujie.liu@intel.com
Signed-off-by: Jan Kara <jack@suse.cz>
        .release                = udf_release_file,
        .fsync                  = generic_file_fsync,
        .splice_read            = generic_file_splice_read,
+       .splice_write           = iter_file_splice_write,
        .llseek                 = generic_file_llseek,
 };