[SCSI] sd: quiet spurious error messages in READ_CAPACITY(16)

sd always tries to submit a READ_CAPACITY(16) CDB,
regardless whether the host actually supports it.
queuecommand() will then return DID_ABORT, which is
not qualified enough to detect the true cause here.
So better check in sd_try_rc16 first if the cdblen
is supported.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>