Apparently, someone changed the gsc driver to allocate one big buffer

at device attach time, instead of allocating and freeing buffers as
necessary. But he or she forgot to remove the line that invalidated
the buffer when the device is closed. Therefore, after using the
device for the first time, the buffer was incorrectly invalidated and
that caused a page fault on the second, and subsequent uses.

Closes PR # kern/2319: Using Genius GS-4500 scanner...

Submitted by:	jmrueda@diatel.upm.es (Javier Martmn Rueda)

sys/i386/isa/gsc.c

@@ -635,7 +635,6 @@ gscclose (dev_t dev, int flags, int fmt, struct proc *p)
 
   outb(scu->ctrl, scu->ctrl_byte & ~GSC_POWER_ON);
 
-  scu->sbuf.base = NULL;
   scu->sbuf.size = INVALID;
   scu->sbuf.poi  = INVALID;