target/ppc: Fix the test raising the decrementer exception

target/ppc: Fix the test raising the decrementer exception

Commit 4d9b8ef9b5ab ("target/ppc: Fix 64-bit decrementer") introduced
new int64t variables and broke the test triggering the decrementer
exception. Revert partially the change to evaluate both clause of the
if statement.

Reported-by: Coverity CID 1464061
Fixes: 4d9b8ef9b5ab ("target/ppc: Fix 64-bit decrementer")
Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20211005053324.441132-1-clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>