clk: imx: 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/20200727200922.GA2326@embeddedorSigned-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/imx/clk-pllv3.c

@@ -433,7 +433,7 @@ struct clk_hw *imx_clk_hw_pllv3(enum imx_pllv3_type type, const char *name,
 		break;
 	case IMX_PLLV3_USB_VF610:
 		pll->div_shift = 1;
-		/* fall through */
+		fallthrough;
 	case IMX_PLLV3_USB:
 		ops = &clk_pllv3_ops;
 		pll->powerup_set = true;
@@ -441,7 +441,7 @@ struct clk_hw *imx_clk_hw_pllv3(enum imx_pllv3_type type, const char *name,
 	case IMX_PLLV3_AV_IMX7:
 		pll->num_offset = PLL_IMX7_NUM_OFFSET;
 		pll->denom_offset = PLL_IMX7_DENOM_OFFSET;
-		/* fall through */
+		fallthrough;
 	case IMX_PLLV3_AV:
 		ops = &clk_pllv3_av_ops;
 		break;