clk: k210: Fix k210_clk_set_parent()

In k210_clk_set_parent(), add missing writel() call to update the mux
register of a clock to change its parent. This also fixes a compilation
warning with clang when compiling with W=1.

Fixes: c6ca761 ("clk: Add RISC-V Canaan Kendryte K210 clock driver")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Link: https://lore.kernel.org/r/20210622064502.14841-1-damien.lemoal@wdc.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

Author: damien-lemoal

drivers/clk/clk-k210.c

@@ -722,6 +722,7 @@ static int k210_clk_set_parent(struct clk_hw *hw, u8 index)
 		reg |= BIT(cfg->mux_bit);
 	else
 		reg &= ~BIT(cfg->mux_bit);
+	writel(reg, ksc->regs + cfg->mux_reg);
 	spin_unlock_irqrestore(&ksc->clk_lock, flags);
 
 	return 0;