percpu: setup_first_chunk rename schunk/dchunk to chunk

There is no need to have the static chunk and dynamic chunk be named
separately as the allocations are sequential. This preemptively solves
the misnomer problem with the base_addrs being moved up in the following
patch. It also removes a ternary operation deciding the first chunk.

Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Tejun Heo <tj@kernel.org>