services: TRNG: Fix -O0 compilation

The code to check for the presence of the TRNG service relies on
toolchain garbage collection, which is not enabled with -O0.

Add #ifdef guards around the call to the TRNG service handler to
cover builds without optimisation as well.

Change-Id: I08ece2005ea1c8fa96afa13904a851dec6b24216
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
1 file changed