mm: minor cleanup of iov_iter_single_seg_count()

The function does not modify iov_iter which 'i' points to.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7617ee0..7d2e893 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -301,7 +301,7 @@
 		struct iov_iter *i, unsigned long offset, size_t bytes);
 void iov_iter_advance(struct iov_iter *i, size_t bytes);
 int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes);
-size_t iov_iter_single_seg_count(struct iov_iter *i);
+size_t iov_iter_single_seg_count(const struct iov_iter *i);
 
 static inline void iov_iter_init(struct iov_iter *i,
 			const struct iovec *iov, unsigned long nr_segs,
diff --git a/mm/filemap.c b/mm/filemap.c
index 83efee7..24a7ea5 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2056,7 +2056,7 @@
 /*
  * Return the count of just the current iov_iter segment.
  */
-size_t iov_iter_single_seg_count(struct iov_iter *i)
+size_t iov_iter_single_seg_count(const struct iov_iter *i)
 {
 	const struct iovec *iov = i->iov;
 	if (i->nr_segs == 1)