spi.c:scan_boardinfo() mustn't be __init_or_module

WARNING: drivers/built-in.o(.text+0x889735): Section mismatch: reference to .init.text:scan_boardinfo (between 'spi_register_master' and '__unregister')

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>