expo: Rename exp_set_text_mode()

Rename this function to match its peers, using the full "expo' prefix.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/boot/expo.c b/test/boot/expo.c
index 56a22ba..70750d3 100644
--- a/test/boot/expo.c
+++ b/test/boot/expo.c
@@ -507,7 +507,7 @@
 	ut_assert_console_end();
 
 	/* now try in text mode */
-	exp_set_text_mode(exp, true);
+	expo_set_text_mode(exp, true);
 	ut_assertok(expo_render(exp));
 
 	ut_assert_nextline("U-Boot    :    Boot Menu");