When run on the wrong platform, the shark_pci_init function
returns an undefined value, as reported by a gcc warning,
so let's just return -ENODEV.
Without this patch, building shark_defconfig results in:
arch/arm/mach-shark/pci.c: In function 'shark_pci_init':
arch/arm/mach-shark/pci.c:42:3: warning: 'return' with no value, in function returning non-void [-Wreturn-type]