ARM: shark: fix shark_pci_init return code

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]

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: "Krzysztof Halasa" <khc@pm.waw.pl>