bdev/raid: Call deconfigure() once at the end of remove_base_devices()

This is a preparation to add completion callback to the
destroy_raid_bdev RPC.

Move the call raid_bdev_deconfigure() to the end of the function.
This will make us to add the callback to raid_bdev_deconfigure()
and remove_base_devices().

Change-Id: Ic8ce847068f5a3682003707c87c364ed4b68e587
Signed-off-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/450569


Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>