ArmPkg/ArmTrngLib: Fix incorrect GUID reference in DEBUG() output

ArmTrngLib crashes when run in DEBUG mode due to the fact that it passed
the [truncated] GUID value to a DEBUG() print statement instead of a
pointer to the GUID which is what the %g conversion expects.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>