tests: mgmt_v3_locks.t fix

this patch fixes a small issue introduced by http://review.gluster.org/#/c/9114/

Change-Id: I42a91544fad2b5f8af70670e4c4cadcac094dd05
BUG: 1163543
Signed-off-by: Atin Mukherjee <amukherj@redhat.com>
Reviewed-on: http://review.gluster.org/9171
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: 长财 余 <einstcrazy@gmail.com>
Reviewed-by: Kaushal M <kaushal@redhat.com>

tests/basic/mgmt_v3-locks.t

@@ -70,7 +70,7 @@ function same_vol_remove_brick {
         local vol=$1
         local brick=$2
         $CLI_1 volume remove-brick $1 $2 start &
-        PID =$!
+        PID=$!
         $CLI_2 volume remove-brick $1 $2 start
         wait $PID
 }