clocksource/drivers/timer-pxa: Rename the file for consistency

For the sake of consistency, let's rename the file to a name similar
to other file names in this directory.
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/Makefile

@@ -29,7 +29,7 @@ obj-$(CONFIG_BCM2835_TIMER)	+= bcm2835_timer.o
 obj-$(CONFIG_CLPS711X_TIMER)	+= clps711x-timer.o
 obj-$(CONFIG_ATLAS7_TIMER)	+= timer-atlas7.o
 obj-$(CONFIG_MXS_TIMER)		+= mxs_timer.o
-obj-$(CONFIG_CLKSRC_PXA)	+= pxa_timer.o
+obj-$(CONFIG_CLKSRC_PXA)	+= timer-pxa.o
 obj-$(CONFIG_PRIMA2_TIMER)	+= timer-prima2.o
 obj-$(CONFIG_U300_TIMER)	+= timer-u300.o
 obj-$(CONFIG_SUN4I_TIMER)	+= timer-sun4i.o