DynamicTablesPkg: Fix unaligned pointers usage

DynamicTablesPkg: Fix unaligned pointers usage

The VS2017 compiler reports 'warning C4366: The result of
the unary '&' operator may be unaligned' if an address of
an unaligned structure member is passed as an argument to
a function.

Fix this warning by using local variables in place of
unaligned structure members.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Alexei Fedorov <Alexei.Fedorov@arm.com>