dmi: Fix build breakage

Commit d7b1956f ("DMI: Introduce
dmi_first_match to make the interface more flexible") introduced compile
errors like the following when !CONFIG_DMI

    drivers/ata/sata_sil.c: In function 'sil_broken_system_poweroff':
    drivers/ata/sata_sil.c:713: error: implicit declaration of function 'dmi_first_match'
    drivers/ata/sata_sil.c:713: warning: initialization makes pointer from integer without a cast

We just need a dummy version of dmi_first_match() to fix this all up.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>