SecurityPkg/RngDxe: Correctly update mAvailableAlgoArrayCount

mAvailableAlgoArrayCount holds the count of available RNG algorithms.
In a following patch, its value will be used to prevent the
EFI_RNG_PROTOCOL to be installed if no RNG algorithm is available.

Correctly set/reset the value for all implementations.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>

SecurityPkg/RandomNumberGenerator/RngDxe/ArmRngDxe.c

@@ -40,6 +40,7 @@ FreeAvailableAlgorithms (
   VOID
   )
 {
+  mAvailableAlgoArrayCount = 0;
   FreePool (mAvailableAlgoArray);
   return;
 }