[PATCH] sata_sil: replace sil_3112_m15w board id with sil_3112

All 3112's have m15w.  Replace sil_3112_m15w with sil_3112 and flag
sil_3112 with SIL_FLAG_MOD15WRITE.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Carlos Pardo <Carlos.Pardo@siliconimage.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>