mlx4_core: Use the right function to free eq->page_list entries

Fix the memory release function to be consistent with the memory
allocation one to prevent problems if the implementation of
pci_free_consistent() and dma_free_coherent() are different.

Signed-off-by: Dotan Barak <dotanb@dev.mellanox.co.il>
Reviewed-by: Eli Cohen <eli@mellanox.co.il>
Signed-off-by: Roland Dreier <roland@purestorage.com>