scsi: sd: Fix typo in sd_first_printk()

Commit b2bff6ce

 ("[SCSI] sd: Quiesce mode sense error messages")
added the macro sd_first_printk(). The macro takes "sdsk" as argument
but dereferences "sdkp". This hasn't caused any real issues since all
callers of sd_first_printk() have an sdkp. But fix the typo.

[mkp: Turned this into a real patch and tweaked commit description]

Signed-off-by: Dietmar Hahn <dietmar.hahn@ts.fujitsu.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>