staging: kpc2000: fix build error on xtensa

kpc2000/kpc_dma/fileops.c includes asm/uaccess.h instead of
linux/uaccess.h, which results in the following build error on xtensa
architecture:

  In file included from
  drivers/staging/kpc2000/kpc_dma/fileops.c:11:
  arch/xtensa/include/asm/uaccess.h:
  In function ‘clear_user’:
  arch/xtensa/include/asm/uaccess.h:40:22:
  error: implicit declaration of function ‘uaccess_kernel’; ...
   #define __kernel_ok (uaccess_kernel())
                        ^~~~~~~~~~~~~~

Include linux/uaccess.h to fix that.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/kpc2000/kpc_dma/fileops.c

@@ -8,7 +8,7 @@
 #include <linux/errno.h>    /* error codes */
 #include <linux/types.h>    /* size_t */
 #include <linux/cdev.h>
-#include <asm/uaccess.h>    /* copy_*_user */
+#include <linux/uaccess.h>  /* copy_*_user */
 #include <linux/aio.h>      /* aio stuff */
 #include <linux/highmem.h>
 #include <linux/pagemap.h>