treewide: Use stdio file descriptor constants

The numeric constants for stdout and stderr are used in a couple of
places, replace them with the friendlier constants.

Signed-off-by: Bjorn Andersson <bjorn.andersson@oss.qualcomm.com>

cdba.c

@@ -834,9 +834,9 @@ int main(int argc, char **argv)
 			const char blue[] = "\033[94m";
 			const char reset[] = "\033[0m";
 
-			write(2, blue, sizeof(blue) - 1);
-			write(2, buf, n);
-			write(2, reset, sizeof(reset) - 1);
+			write(STDERR_FILENO, blue, sizeof(blue) - 1);
+			write(STDERR_FILENO, buf, n);
+			write(STDERR_FILENO, reset, sizeof(reset) - 1);
 
 			bump_inactivity_timer = true;
 		}

drivers/external.c

@@ -29,7 +29,7 @@ static int external_helper(struct external *ext, const char *command, bool on)
 	switch (pid) {
 	case 0:
 		/* Do not clobber stdout with program messages or cdba will become confused */
-		dup2(2, 1);
+		dup2(STDERR_FILENO, STDOUT_FILENO);
 		return execlp(ext->path, ext->path, ext->board, command, on ? "on": "off", NULL);
 	case -1:
 		return -1;