x86: Tidy up VESA mode numbers

There are some bits which should be ignored when displaying the mode number.
Make sure that they are not included in the mode that is displayed.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/lib/bios.c b/arch/x86/lib/bios.c
index 4285348..1d75cfc 100644
--- a/arch/x86/lib/bios.c
+++ b/arch/x86/lib/bios.c
@@ -207,12 +207,14 @@
 
 static u8 vbe_set_mode(struct vbe_mode_info *mi)
 {
-	debug("VBE: Setting VESA mode %#04x\n", mi->video_mode);
+	int video_mode = mi->video_mode;
+
+	debug("VBE: Setting VESA mode %#04x\n", video_mode);
 	/* request linear framebuffer mode */
-	mi->video_mode |= (1 << 14);
+	video_mode |= (1 << 14);
 	/* don't clear the framebuffer, we do that later */
-	mi->video_mode |= (1 << 15);
-	realmode_interrupt(0x10, VESA_SET_MODE, mi->video_mode,
+	video_mode |= (1 << 15);
+	realmode_interrupt(0x10, VESA_SET_MODE, video_mode,
 			   0x0000, 0x0000, 0x0000, 0x0000);
 
 	return 0;
@@ -236,6 +238,7 @@
 		return;
 	}
 
+	mode_info->video_mode &= 0x3ff;
 	vbe_set_mode(mode_info);
 }