clk: sunxi: remove unused variable

The only use of the local num_parents variable was remove,
so we now get a warning:

drivers/clk/sunxi/clk-sun4i-tcon-ch1.c: In function 'tcon_ch1_get_parent':
drivers/clk/sunxi/clk-sun4i-tcon-ch1.c:82:6: error: unused variable 'num_parents' [-Werror=unused-variable]

This removes the variable.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 4de2d58bc973 ("clk: sunxi: tcon-ch1: Do not return a negative error in get_parent")
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>