ctl ramdisk: Free compare buffer after a compare I/O request.

For a compare request, the ramdisk backend allocates a temporary
buffer to hold the I/O data and then compares it against the LUN's
pages in ctl_backend_ramdisk_cmp after the data has been filled.
However, the tempory buffer was leaked when after the comparison was
complete.  Fix this by freeing the buffer after the comparison.

Reviewed by:	mav
Sponsored by:	Chelsio Communications
Differential Revision:	https://reviews.freebsd.org/D34316

sys/cam/ctl/ctl_backend_ramdisk.c

@@ -386,6 +386,7 @@ ctl_backend_ramdisk_cmp(union ctl_io *io)
 		if (res < cbe_lun->blocksize)
 			break;
 	}
+	free(io->scsiio.kern_data_ptr, M_RAMDISK);
 	if (lbas > 0) {
 		off += io->scsiio.kern_rel_offset - io->scsiio.kern_data_len;
 		scsi_u64to8b(off, info);