mm/mm_init.c: clean code. Use BUILD_BUG_ON when comparing compile time constant

MAX_ZONELISTS is a compile time constant, so it should be compared using
BUILD_BUG_ON not BUG_ON.

Signed-off-by: Mateusz Nosek <mateusznosek0@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Link: http://lkml.kernel.org/r/20200228224617.11343-1-mateusznosek0@gmail.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>