clk: sunxi: remove stale Makefile entry

Patch 85a18198 "clk: sunxi: Use common of_clk_init() function"
removed the clk-sunxi.c file but left the Makefile entry, which
causes a build error in multi_v7_defconfig:

make[4]: *** No rule to make target `drivers/clk/clk-sunxi.o', needed by `drivers/clk/built-in.o'.

The obvious fix is to remove the extraneous line from the
Makefile.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Prashant Gaikwad <pgaikwad@nvidia.com>
Cc: Maxime Ripard <maxime.ripard@anandra.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>