malloc: fix style in free list index computation

malloc: fix style in free list index computation

Cleanup code style issue reported by kernel checkpatch. As follows:
  * ERROR:CODE_INDENT: code indent should use tabs where possible
  * ERROR:SPACING: spaces required around that '?' (ctx:VxE)
  * WARNING:INDENTED_LABEL: labels should not be indented

Fixes: b0489e7bca2f ("malloc: fix linear complexity")
Cc: stable@dpdk.org
Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>