soc: renesas: rcar-sysc: Remove unneeded inclusion of <linux/bug.h>

No R-Car or RZ/G SYSC driver uses any of the definitions provided by
<linux/bug.h>, hence there is no need to include this header file.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Link: https://lore.kernel.org/r/20190920144705.27394-1-geert+renesas@glider.be