cxgb4: fix a memory leak bug

In blocked_fl_write(), 't' is not deallocated if bitmap_parse_user() fails,
leading to a memory leak bug. To fix this issue, free t before returning
the error.

Signed-off-by: Wenwen Wang <wenwen@cs.uga.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>