Change the getline return type to match its declaration.

Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>

diff -urN sed-4.1.2-orig/lib/getline.c sed-4.1.2/lib/getline.c
--- sed-4.1.2-orig/lib/getline.c	2010-08-31 08:47:50.070094024 +0800
+++ sed-4.1.2/lib/getline.c	2010-08-31 08:48:50.982178172 +0800
@@ -30,7 +30,7 @@
    necessary.  Returns the number of characters read (not including the
    null terminator), or -1 on error or EOF.  */
 
-size_t
+ssize_t
 getline (lineptr, n, stream)
      char **lineptr;
      size_t *n;
