[PATCH] macintosh: tidy-up driver_register() return values

Remove the assumption that driver_register() returns the number of devices
bound to the driver.  In fact, it returns zero for success or a negative
error value.

All callers of macio_register_driver() either ignore the return value or
return it as the return value of a module_init() function.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>