switch simple cases of fget_light to fdget

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/mm/readahead.c b/mm/readahead.c
index 1011111..7963f23 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -579,20 +579,19 @@
 SYSCALL_DEFINE(readahead)(int fd, loff_t offset, size_t count)
 {
 	ssize_t ret;
-	struct file *file;
-	int fput_needed;
+	struct fd f;
 
 	ret = -EBADF;
-	file = fget_light(fd, &fput_needed);
-	if (file) {
-		if (file->f_mode & FMODE_READ) {
-			struct address_space *mapping = file->f_mapping;
+	f = fdget(fd);
+	if (f.file) {
+		if (f.file->f_mode & FMODE_READ) {
+			struct address_space *mapping = f.file->f_mapping;
 			pgoff_t start = offset >> PAGE_CACHE_SHIFT;
 			pgoff_t end = (offset + count - 1) >> PAGE_CACHE_SHIFT;
 			unsigned long len = end - start + 1;
-			ret = do_readahead(mapping, file, start, len);
+			ret = do_readahead(mapping, f.file, start, len);
 		}
-		fput_light(file, fput_needed);
+		fdput(f);
 	}
 	return ret;
 }