clocksource/drivers/riscv: Change name riscv_timer to timer-riscv

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

drivers/clocksource/Makefile

@@ -78,6 +78,6 @@ obj-$(CONFIG_H8300_TPU)			+= h8300_tpu.o
 obj-$(CONFIG_CLKSRC_ST_LPC)		+= clksrc_st_lpc.o
 obj-$(CONFIG_X86_NUMACHIP)		+= numachip.o
 obj-$(CONFIG_ATCPIT100_TIMER)		+= timer-atcpit100.o
-obj-$(CONFIG_RISCV_TIMER)		+= riscv_timer.o
+obj-$(CONFIG_RISCV_TIMER)		+= timer-riscv.o
 obj-$(CONFIG_CSKY_MP_TIMER)		+= timer-mp-csky.o
 obj-$(CONFIG_GX6605S_TIMER)		+= timer-gx6605s.o