cxgb4: Fix some small bugs in t4_sge_init_soft() when our Page Size is 64KB

We'd come in with SGE_FL_BUFFER_SIZE[0] and [1] both equal to 64KB and the
extant logic would flag that as an error.

Based on original work by Casey Leedom <leedom@chelsio.com>

Signed-off-by: Kumar Sanghvi <kumaras@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>