bdev/raid: fix up some whitespace

Signed-off-by: Jim Harris <james.r.harris@intel.com>
Change-Id: Ib47f1b360b7a44b82bbbd8cd51fd6740ba47b25d

Reviewed-on: https://review.gerrithub.io/423405


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Chandler-Test-Pool: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>