target: Change sbc_emulate_noop to return sense_reason_t

As reported by Fengguang Wu + 0 day build team, the sense_reason_t conversion
in for-next did not catch the recent sbc_emulate_noop() addition in mainline,
producing the following build warning in auto-next:

drivers/target/target_core_sbc.c: In function ‘sbc_parse_cdb’:
drivers/target/target_core_sbc.c:555: warning: assignment from incompatible pointer type

Go ahead and remove duplicate sbc_emulate_verify(), and change VERIFY to
use sbc_emulate_noop() as well.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>