clocksource: Fix type confusion for clocksource_mmio_readX_Y

The types' definations are:
   o  cycle_t       -> u64
   o  readl_relaxed -> u32
   o  readw_relaxed -> u16

So let clocksource_mmio_readX_Ys return a cast to cycle_t, though
this maybe look reduntant sometimes, it make sense and they will be
more readable and less confusion...

This patch clarifies the functions type and fix it.
Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/mmio.c

@@ -22,22 +22,22 @@ static inline struct clocksource_mmio *to_mmio_clksrc(struct clocksource *c)
 
 cycle_t clocksource_mmio_readl_up(struct clocksource *c)
 {
-	return readl_relaxed(to_mmio_clksrc(c)->reg);
+	return (cycle_t)readl_relaxed(to_mmio_clksrc(c)->reg);
 }
 
 cycle_t clocksource_mmio_readl_down(struct clocksource *c)
 {
-	return ~readl_relaxed(to_mmio_clksrc(c)->reg);
+	return ~(cycle_t)readl_relaxed(to_mmio_clksrc(c)->reg);
 }
 
 cycle_t clocksource_mmio_readw_up(struct clocksource *c)
 {
-	return readw_relaxed(to_mmio_clksrc(c)->reg);
+	return (cycle_t)readw_relaxed(to_mmio_clksrc(c)->reg);
 }
 
 cycle_t clocksource_mmio_readw_down(struct clocksource *c)
 {
-	return ~(unsigned)readw_relaxed(to_mmio_clksrc(c)->reg);
+	return ~(cycle_t)readw_relaxed(to_mmio_clksrc(c)->reg);
 }
 
 /**