QuarkSocPkg/QncSmmDispatcher: Fix use after free issue

Update Quark North Cluster SMM dispatcher logic to handle
case where an SMI handler unregisters itself.

https://bugzilla.tianocore.org/show_bug.cgi?id=51

This issue was reproduced using the unit test at:

https://github.com/mdkinney/edk2/tree/Bug51/Reproduce

An ASSERT() is generated the 4th time the periodic SMI
handler is triggered when the periodic SMI handler
unregisters itself.  After applying this patch, the
DEBUG() message from the periodic SMI handler in this
unit test is generated 4 times, the periodic SMI handler
is unregistered, and the UEFI Shell works as expected.

Cc: Kelly Steele <kelly.steele@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Michael Kinney <michael.d.kinney@intel.com>
Reviewed-by: Kelly Steele <kelly.steele@intel.com>