clk: davinci: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1].

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-throughSigned-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20200727201122.GA2593@embeddedorReviewed-by: David Lechner <david@lechnology.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/davinci/pll.c

@@ -651,7 +651,7 @@ static int davinci_pll_sysclk_rate_change(struct notifier_block *nb,
 		pllcmd = readl(pll->base + PLLCMD);
 		pllcmd |= PLLCMD_GOSET;
 		writel(pllcmd, pll->base + PLLCMD);
-		/* fallthrough */
+		fallthrough;
 	case PRE_RATE_CHANGE:
 		/* Wait until for outstanding changes to take effect */
 		do {