[SCSI] sr: fix error code check in sr_block_ioctl()

sr_block_ioctl() should proceed to SCSI ioctls if cdrom_ioctl()
returns -ENOSYS.  However it tested for ENOSYS instead of -ENOSYS
rendering all SCSI ioctls other than GET_IDLUN and GET_BUS_NUMBER
inaccessible.  Fix it.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>