soc: fsl: qbman: qman: Remove unused variable 'dequeue_wq'

Fixes the following W=1 kernel build warning(s):

 drivers/soc/fsl/qbman/qman.c: In function ‘qman_shutdown_fq’:
 drivers/soc/fsl/qbman/qman.c:2700:8: warning: variable ‘dequeue_wq’ set but not used [-Wunused-but-set-variable]

Cc: Li Yang <leoyang.li@nxp.com>
Cc: YueHaibing <yuehaibing@huawei.com>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Li Yang <leoyang.li@nxp.com>