sem_open(): Fix a compiler error introduced with the setvbuf() changes.

fs/semaphore/sem_open.c

@@ -142,7 +142,6 @@ FAR sem_t *sem_open (FAR const char *name, int oflags, ...)
       /* Something exists at this path.  Get the search results */
 
       inode = desc.node;
-      relpath = desc.relpath;
       DEBUGASSERT(inode != NULL);
 
       /* Verify that the inode is a semaphore */

libc/Kconfig

@@ -14,9 +14,10 @@ config STDIO_DISABLE_BUFFERING
 
 		NOTE that even if STDIO buffering is enabled, you can still disable
 		buffer by setting CONFIG_STDIO_BUFFER_SIZE=0 or dynamically through
-		the setvbuf() interface.  In these case, however, there is no
-		reduction in code size.  Only setting CONFIG_STDIO_DISABLE_BUFFERING
-		will reduce code size.
+		the setvbuf() interface.  In this case, however,  memory used for
+		buffering will be eliminated, of course, buth there will be no
+		reduction in static code size.  Only setting
+		CONFIG_STDIO_DISABLE_BUFFERING will reduce static code size.
 
 if !STDIO_DISABLE_BUFFERING