sparc: Ignore drivers/video/console/promcon_tbl.c conmakehash generated file

Add drivers/video/console/promcon_tbl.c to the list of ignored files.
This file is generated by conmakehash against drivers/video/console/prom.uni.

Signed-off-by: Florian Fainelli <florian.fainelli@telecomint.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>