QEMU i486: Minor updates to VGA driver

arch/x86/src/qemu/Kconfig

@@ -19,4 +19,10 @@ config QEMU_VGA
 	---help---
 		Enable support for the QEMU VGA.  See qemu_vga.h for interfaces.
 
+		NOTE:  This VGA driver exports a character driver that can be used
+		to write into the VGA framebuffer. It does *NOT* support a NuttX
+		framebuffer interfaces and, hence, cannot be used with the NuttX
+		graphics subsystem.  Such a conversion to the standard NuttX
+		framebuffer interface would, however, not be a big job.
+
 endif

arch/x86/src/qemu/qemu_vga.c

@@ -458,6 +458,9 @@ static off_t vga_seek(FAR struct file *filp, off_t offset, int whence)
       case SEEK_END:  /* From the end of the file */
         newpos = (VGA_FBSIZE - 1) - offset;
         break;
+
+      default:
+        return g_curpos;
     }
 
   /* Make sure that the new cursor position lies within the frame buffer */