drivers/block/nvme-core.c: fix build with gcc-4.4.4

gcc-4.4.4 (and possibly other versions) fail the compile when initializers
are used with anonymous unions.  Work around this.

drivers/block/nvme-core.c: In function 'nvme_identify_ctrl':
drivers/block/nvme-core.c:1163: error: unknown field 'identify' specified in initializer
drivers/block/nvme-core.c:1163: warning: missing braces around initializer
drivers/block/nvme-core.c:1163: warning: (near initialization for 'c.<anonymous>')
drivers/block/nvme-core.c:1164: error: unknown field 'identify' specified in initializer
drivers/block/nvme-core.c:1164: warning: excess elements in struct initializer
drivers/block/nvme-core.c:1164: warning: (near initialization for 'c')
...

This patch has no effect on text size with gcc-4.8.2.

Fixes: d29ec824 ("nvme: submit internal commands through the block layer")
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <axboe@fb.com>