[SCSI] Disable sym2 driver queueing

Undef SYM_OPT_HANDLE_DEVICE_QUEUEING.
Call sym_put_start_queue instead of sym_start_next_ccbs.
Turn asserts into checks that we can send the command to the adapter,
and return busy from queuecommand if we can't.

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>