tidy up O_NONBLOCK usage. use libbb functions in stty.

Added O_RDONLY where improves readability. Note: O_RDONLY == 0,
so it is there even if not specified.

function                                             old     new   delta
stty_main                                           1289    1235     -54

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/libbb/xfuncs.c b/libbb/xfuncs.c
index e47b01d..aac46f4 100644
--- a/libbb/xfuncs.c
+++ b/libbb/xfuncs.c
@@ -27,12 +27,12 @@
 /* Turn on nonblocking I/O on a fd */
 int FAST_FUNC ndelay_on(int fd)
 {
-	return fcntl(fd, F_SETFL, fcntl(fd,F_GETFL) | O_NONBLOCK);
+	return fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK);
 }
 
 int FAST_FUNC ndelay_off(int fd)
 {
-	return fcntl(fd, F_SETFL, fcntl(fd,F_GETFL) & ~O_NONBLOCK);
+	return fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) & ~O_NONBLOCK);
 }
 
 int FAST_FUNC close_on_exec_on(int fd)