net/mlx5e: Wait for RX buffers initialization in a more proper manner

Use jiffies rather than wait loop with msleep().

The wait loop didn't take into consideration time when the
process was not executing.

Signed-off-by: Achiad Shochat <achiad@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>