drivers: net: xgene-v2: misc fixes

Fixed review comments from the previous patch-set.

- changed return value check of platform_get_irq() to < 0
- replaced devm_request(free)_irq() calls by request(free)_irq() since
  they are called from open() and close()
- changed sizeof(struct mystruct) to sizeof(*mystruct)
- reduced indentation on tx_timeout()

Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>