net: mvpp2: drop useless fields in mvpp2_bm_pool and related code

This commit drops dead code from the mvpp2 driver. The 'in_use' and
'in_use_thresh' fields of 'struct mvpp2_bm_pool' are
incremented/decremented/initialized in various places. But they are only
used in one place:

       if (is_recycle &&
           (atomic_read(&bm_pool->in_use) < bm_pool->in_use_thresh))
               return 0;

However 'is_recycle', passed as argument to mvpp2_rx_refill() is always
false. So in fact, this code is never reached, and the 'is_recycle'
argument is useless. So let's drop this code.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>