net: mvpp2: remove mvpp2_pool_refill()

When all a function does is calling another function with the exact same
arguments, in the exact same order, you know it's time to remove said
function. Which is exactly what this commit does.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>