clk: rockchip: fix warning reported by kernel-doc

./scripts/kernel-doc -man -v drivers/clk/rockchip/clk.h > /dev/null

drivers/clk/rockchip/clk.h:133: warning: missing initial short
description on line:
 * struct rockchip_clk_provider: information about clock provider
drivers/clk/rockchip/clk.h:133: info: Scanning doc for struct
drivers/clk/rockchip/clk.h:164: warning: missing initial short
description on line:
 * struct rockchip_pll_clock: information about pll clock
drivers/clk/rockchip/clk.h:164: info: Scanning doc for struct
drivers/clk/rockchip/clk.h:194: warning: No description found for
parameter 'parent_names'
drivers/clk/rockchip/clk.h:194: warning: No description found for
parameter 'num_parents'
drivers/clk/rockchip/clk.h:194: warning: Excess struct/union/enum/typedef
member 'parent_name' description in 'rockchip_pll_clock'
drivers/clk/rockchip/clk.h:235: warning: missing initial short
description on line:
 * struct rockchip_cpuclk_reg_data: describes register offsets and
masks of the cpuclock

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>