clocksource/drivers/tegra20: Change name tegra20_timer to timer-tegra20

In order to unify the names in this directory, let's rename the driver to be
prefixed with timer-*
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/Makefile

@@ -35,7 +35,7 @@ obj-$(CONFIG_U300_TIMER)	+= timer-u300.o
 obj-$(CONFIG_SUN4I_TIMER)	+= sun4i_timer.o
 obj-$(CONFIG_SUN5I_HSTIMER)	+= timer-sun5i.o
 obj-$(CONFIG_MESON6_TIMER)	+= meson6_timer.o
-obj-$(CONFIG_TEGRA_TIMER)	+= tegra20_timer.o
+obj-$(CONFIG_TEGRA_TIMER)	+= timer-tegra20.o
 obj-$(CONFIG_VT8500_TIMER)	+= timer-vt8500.o
 obj-$(CONFIG_NSPIRE_TIMER)	+= timer-zevio.o
 obj-$(CONFIG_BCM_KONA_TIMER)	+= bcm_kona_timer.o