libcxgb: fix incorrect ppmax calculation

BITS_TO_LONGS() uses DIV_ROUND_UP() because of
this ppmax value can be greater than available
per cpu page pods.

This patch removes BITS_TO_LONGS() to fix this
issue.

Signed-off-by: Varun Prakash <varun@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>