cxgb4: avoid accessing registers when clearing filters

Hardware register having the server TID base can contain
invalid values when adapter is in bad state (for example,
due to AER fatal error). Reading these invalid values in the
register can lead to out-of-bound memory access. So, fix
by using the saved server TID base when clearing filters.

Fixes: b1a79360

 ("cxgb4: Delete all hash and TCAM filters before resource cleanup")
Signed-off-by: Raju Rangoju <rajur@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>