target/ppc: PMU do not clear MMCR0[FCECE] on performance monitor alert

FCECE does not get cleared according to the ISA v3.1B.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20230530134313.387252-1-npiggin@gmail.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>

target/ppc/power8-pmu.c

@@ -289,7 +289,6 @@ static void fire_PMC_interrupt(PowerPCCPU *cpu)
     pmu_update_cycles(env);
 
     if (env->spr[SPR_POWER_MMCR0] & MMCR0_FCECE) {
-        env->spr[SPR_POWER_MMCR0] &= ~MMCR0_FCECE;
         env->spr[SPR_POWER_MMCR0] |= MMCR0_FC;
 
         /* Changing MMCR0_FC requires summaries and hflags update */