It's not a problem of case sensivity.
It's a feature of system view ACCESSIBLE_VIEWS.
Definition:
ACCESSIBLE_VIEWS
Accessible views for a given user
This means: You are only allowed to select from this view if you add a 'USER_NAME = ...' in the where condition.
A 'where upper(USER_NAME) = ...' doesn't qualify.
For your problem you should consider a quite different approach, if you need case insensivity at all.
As far as I know user names in HANA aren't case sensitive.
'system' and 'SYSTEM' simply are the same user.
regards