net: ethernet: mlx4: Fix memory allocation in mlx4_buddy_init()

On machines with much memory (> 2 TByte) and log_mtts_per_seg == 0, a
max_order of 31 will be passed to mlx_buddy_init(), which results in
s = BITS_TO_LONGS(1 << 31) becoming a negative value, leading to
kvmalloc_array() failure when it is converted to size_t.

  mlx4_core 0000:b1:00.0: Failed to initialize memory region table, aborting
  mlx4_core: probe of 0000:b1:00.0 failed with error -12

Fix this issue by changing the left shifting operand from a signed literal to
an unsigned one.

Fixes: 225c7b1f ("IB/mlx4: Add a driver Mellanox ConnectX InfiniBand adapters")
Signed-off-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>