fix(runtime/rmi) : remove redundant granule_unlock

- The aux granules are unlocked as part of granule_unlock_transition(),
  calling granule_unlock() again causes assertion since
  granule_get_state() api inside granule_unlock() expects the granule
  to be in locked state.

Signed-off-by: Shyamanth RH <shyamanth.rh@arm.com>
Change-Id: I3ccbfacdf40b3202baa43fa2ad1dcf62d5a0cd1b