armv7m: Remove unused armv7m_nvic_acknowledge_irq() return value

Having armv7m_nvic_acknowledge_irq() return the new value of
env->v7m.exception and its one caller assign the return value
back to env->v7m.exception is pointless. Just make the return
type void instead.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>

hw/intc/armv7m_nvic.c

@@ -412,7 +412,7 @@ void armv7m_nvic_set_pending(void *opaque, int irq)
 }
 
 /* Make pending IRQ active.  */
-int armv7m_nvic_acknowledge_irq(void *opaque)
+void armv7m_nvic_acknowledge_irq(void *opaque)
 {
     NVICState *s = (NVICState *)opaque;
     CPUARMState *env = &s->cpu->env;
@@ -439,8 +439,6 @@ int armv7m_nvic_acknowledge_irq(void *opaque)
     env->v7m.exception = s->vectpending;
 
     nvic_irq_update(s);
-
-    return env->v7m.exception;
 }
 
 void armv7m_nvic_complete_irq(void *opaque, int irq)

target/arm/cpu.h

@@ -1365,7 +1365,7 @@ static inline bool armv7m_nvic_can_take_pending_exception(void *opaque)
 }
 #endif
 void armv7m_nvic_set_pending(void *opaque, int irq);
-int armv7m_nvic_acknowledge_irq(void *opaque);
+void armv7m_nvic_acknowledge_irq(void *opaque);
 void armv7m_nvic_complete_irq(void *opaque, int irq);
 
 /* Interface for defining coprocessor registers.

target/arm/helper.c

@@ -6142,7 +6142,7 @@ void arm_v7m_cpu_do_interrupt(CPUState *cs)
         armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_DEBUG);
         return;
     case EXCP_IRQ:
-        env->v7m.exception = armv7m_nvic_acknowledge_irq(env->nvic);
+        armv7m_nvic_acknowledge_irq(env->nvic);
         break;
     case EXCP_EXCEPTION_EXIT:
         do_v7m_exception_exit(env);