Use const for the opal_fd_write() function, just to be nice.

This commit was SVN r23452.

opal/util/fd.c

@@ -44,10 +44,10 @@ int opal_fd_read(int fd, int len, void *buffer)
 /*
  * Simple loop over writing to an fd
  */
-int opal_fd_write(int fd, int len, void *buffer)
+int opal_fd_write(int fd, int len, const void *buffer)
 {
     int rc;
-    char *b = buffer;
+    const char *b = buffer;
 
     while (len > 0) {
         rc = write(fd, b, len);

opal/util/fd.h

@@ -44,6 +44,6 @@ OPAL_DECLSPEC int opal_fd_read(int fd, int len, void *buffer);
  * Loop over writing to the fd until len bytes are written or an error
  * occurs.  EAGAIN and EINTR are transparently handled.
  */
-OPAL_DECLSPEC int opal_fd_write(int fd, int len, void *buffer);
+OPAL_DECLSPEC int opal_fd_write(int fd, int len, const void *buffer);
 
 #endif