block: kmalloc args reversed, small function definition fixes

Noticed by sparse:
block/blk-softirq.c:156:12: warning: symbol 'blk_softirq_init' was not declared. Should it be static?
block/genhd.c:583:28: warning: function 'bdget_disk' with external linkage has definition
block/genhd.c:659:17: warning: incorrect type in argument 1 (different base types)
block/genhd.c:659:17:    expected unsigned int [unsigned] [usertype] size
block/genhd.c:659:17:    got restricted gfp_t
block/genhd.c:659:29: warning: incorrect type in argument 2 (different base types)
block/genhd.c:659:29:    expected restricted gfp_t [usertype] flags
block/genhd.c:659:29:    got unsigned int
block: kmalloc args reversed

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>