staging: xillybus: XILLYBUS_PCIE depends on PCI_MSI

xillybus_pcie.c will compile and load properly on PCI only, but will do
nothing useful without PCI_MSI.

PCI_MSI depends on PCI, so depending on PCI_MSI covers both.

Signed-off-by: Eli Billauer <eli.billauer@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>