enic: fix build with gcc < 4.4

enic: fix build with gcc < 4.4

gcc4.3 will raise warnings in blow code for initialized field overwritten.

enic_main.c: In function ‘enic_set_rsskey’:
enic_main.c:845: error: initialized field overwritten
enic_main.c:845: error: (near initialization for ‘rss_key.key’)
enic_main.c:846: error: initialized field overwritten
enic_main.c:846: error: (near initialization for ‘rss_key.key’)
enic_main.c:847: error: initialized field overwritten
enic_main.c:847: error: (near initialization for ‘rss_key.key’)

static union vnic_rss_key rss_key = {
	.key[0] = ...,
	.key[1] = ...,
	.key[2] = ...,
	.key[3] = ...,
};

Change struct initialized code reference to ISO 9899 section 6.7.8.
gcc4.3 will happy for that.

static union vnic_rss_key rss_key = {
	.key = {
		[0] = ...,
		[1] = ...,
		[2] = ...,
		[3] = ...,
	}

Signed-off-by: Marvin Liu <yong.liu@intel.com>