staging: staging: kpc2000: kpc_dma: fix symbol 'kpc_dma_add_device' was not declared.

This was reported by sparse:
drivers/staging/kpc2000/kpc_dma/kpc_dma_driver.c:39:7: warning: symbol 'kpc_dma_add_device
' was not declared. Should it be static?

Signed-off-by: Valerio Genovese <valerio.click@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>