LU-15263 quota: fix bug in qmt_pool_recalc

LU-15263 quota: fix bug in qmt_pool_recalc

env should be freed at the end of qmt_pool_recalc,
as it is needed in qpi_putref. It causes a panic,
if pool has the last reference:
    BUG: unable to handle NULL pointer dereference at 000000000000a0
    IP: lu_context_key_get+0x17/0x30 [obdclass]
    Call Trace:
      lu_object_free.isra.30+0x68/0x170 [obdclass]
      lu_object_put+0xc5/0x3e0 [obdclass]
      qmt_pool_free+0x30c/0x590 [lquota]
      qmt_pool_recalc+0x365/0x1260 [lquota]
      kthread+0xd1/0xe0
      ret_from_fork_nospec_begin+0x21/0x21

Lustre-change: https://review.whamcloud.com/45632
Lustre-commit: 57d88137e12472cf5ea08aa28957b4767abd475c

HPE-bug-id: LUS-10426
Change-Id: Ic23dcb858ff811757f38948aa572c936c076e21e
Signed-off-by: Sergey Cheremencev <sergey.cheremencev@hpe.com>
Reviewed-by: Vladimir Saveliev <vlaidimir.saveliev@hpe.com>
Reviewed-by: Andriy Skulysh <c17819@cray.com>
Reviewed-by: Andriy Skulysh <andriy.skulysh@hpe.com>
Reviewed-on: https://review.whamcloud.com/46794
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>