rrunner.c:rr_init() must be __devinit

This patch fixes the following section mismatch:

<--  snip  -->

...
  MODPOST vmlinux
WARNING: drivers/built-in.o(.text+0x26e3f2): Section mismatch: reference to .init.text:rr_init (between 'rr_init_one' and 'rr_remove_one')
...

<--  snip  -->

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Jeff Garzik <jeff@garzik.org>