hostfs: support splice_write

There's really no good reason not to, and e.g. trace-cmd
currently requires it for the temporary per-CPU files.
Hook up splice_write just like everyone else does.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/hostfs/hostfs_kern.c

@@ -381,6 +381,7 @@ static int hostfs_fsync(struct file *file, loff_t start, loff_t end,
 static const struct file_operations hostfs_file_fops = {
 	.llseek		= generic_file_llseek,
 	.splice_read	= generic_file_splice_read,
+	.splice_write	= iter_file_splice_write,
 	.read_iter	= generic_file_read_iter,
 	.write_iter	= generic_file_write_iter,
 	.mmap		= generic_file_mmap,