staging: dgnc: Kconfig: add dependency PCI for it

DGNC is based on PCI, so need add related dependency, or when compiled
with PCI disabled, it will be fail.

The related error (randconfig for PCI disabled under s390):

  drivers/staging/dgnc/dgnc_cls.c:1394:2: error: implicit declaration of function ‘ioremap’ [-Werror=implicit-function-declaration]
  drivers/staging/dgnc/dgnc_cls.c:1407:3: error: implicit declaration of function ‘iounmap’ [-Werror=implicit-function-declaration]

Cc: Lidza Louina <lidza.louina@gmail.com>
Signed-off-by: Chen Gang <gang.chen@asianux.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>