rivafb_setup() must be __devinit

WARNING: drivers/built-in.o(.text+0x57106): Section mismatch: reference to .init.text:rivafb_setup (between 'rivafb_init' and 'nv3Busy')

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>