net/mlx4_en: Fix wrong indentation

Use tabs instead of spaces before if statement, no functional change.

Fixes: e7c1c2c4

 ("mlx4_en: Added self diagnostics test implementation")
Signed-off-by: Kamal Heib <kamalh@mellanox.com>
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>