fix fetch EK request

[gh4683]

In RotateAIK flow and EnrollWithHMACCHallenge flow, we incorrectly call FetchEK with Chassis Serial number instead of supervisor serial number, which resulted in errors while testing. Fixed it by passing in supervisor serial number instead

[coveralls]

Pull Request Test Coverage Report for Build 20833249711

Details

• 6 of 7 (85.71%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 52.958%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
service/biz/enrollz_biz.go	6	7	85.71%

Totals
Change from base Build 20800848059:	0.03%
Covered Lines:	2005
Relevant Lines:	3786

---

💛 - Coveralls

[muntazirsal]

LGTM