ssb: make SSB_PCICORE_HOSTMODE depend on SSB = y

SSB_PCICORE_HOSTMODE protects MIPS specific code that calls not exported
symbols pcibios_enable_device and register_pci_controller. This code is
supposed to be compiled only with ssb builtin.

This fixes:
ERROR: "pcibios_enable_device" [drivers/ssb/ssb.ko] undefined!
ERROR: "register_pci_controller" [drivers/ssb/ssb.ko] undefined!
make[1]: *** [scripts/Makefile.modpost:92: __modpost] Error 1
Reported-by: Matt Redfearn <matt.redfearn@mips.com>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/ssb/Kconfig

@@ -131,7 +131,7 @@ config SSB_DRIVER_PCICORE
 
 config SSB_PCICORE_HOSTMODE
 	bool "Hostmode support for SSB PCI core"
-	depends on SSB_DRIVER_PCICORE && SSB_DRIVER_MIPS
+	depends on SSB_DRIVER_PCICORE && SSB_DRIVER_MIPS && SSB = y
 	help
 	  PCIcore hostmode operation (external PCI bus).