rtlwifi: Return correct failure code on error

Callers of rtl_pci_init expect zero to be returned on error. Returning
the error code leads to, amongst other things, divide by zero panics
attempting to use the ring size that is set to zero.

Signed-off-by: Simon Graham <simon.graham@virtualcomputer.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>