Staging: rts5208: Use module_pci_driver

Macro module_pci_driver is used for drivers whose init
and exit paths does only register and unregister to pci
API. So, here remove some boilerplate code by using
module_pci_driver. Also, change driver to rtsx_driver,
to avoid implicitly redefining driver_init.

Signed-off-by: Vaishali Thakkar <vthakkar1994@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>