Use BUG_ON() instead of an 'if' condition followed by BUG().

The semantic patch that makes this change is available
in scripts/coccinelle/misc/bugon.cocci.

More information about semantic patching is available at
http://coccinelle.lip6.fr/Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>