powerpc/highmem: change BUG_ON() to WARN_ON()

[Michael Ellerman]

On Thu, 2019-03-07 at 09:47:50 UTC, Christophe Leroy wrote:
> In arch/powerpc/mm/highmem.c, BUG_ON() is called only when
> CONFIG_DEBUG_HIGHMEM is selected, this means the BUG_ON() is
> not vital and can be replaced by a a WARN_ON
> 
> At the sametime, use IS_ENABLED() instead of #ifdef to clean a bit.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/6c84f8c5cbfb4bf728f88296bc035c4a

cheers