clk: imx8: Add dummy clk

There is a dummy clk entry for i.MX8QM/QXP, so add the dummy clk enable
and get rate. Otherwise "__imx8_clk_enable(Invalid clk ID #0)".

Fixes: 76332fae769 ("mmc: fsl_esdhc_imx: Enable AHB/IPG clk with clk bulk API")
Reviewed-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Tested-by: Heiko Schocher <hs@denx.de>
diff --git a/drivers/clk/imx/clk-imx8qm.c b/drivers/clk/imx/clk-imx8qm.c
index 62fed7e..466d717 100644
--- a/drivers/clk/imx/clk-imx8qm.c
+++ b/drivers/clk/imx/clk-imx8qm.c
@@ -48,6 +48,8 @@
 	debug("%s(#%lu)\n", __func__, clk->id);
 
 	switch (clk->id) {
+	case IMX8QM_CLK_DUMMY:
+		return 0;
 	case IMX8QM_A53_DIV:
 		resource = SC_R_A53;
 		pm_clk = SC_PM_CLK_CPU;
@@ -264,6 +266,8 @@
 	debug("%s(#%lu)\n", __func__, clk->id);
 
 	switch (clk->id) {
+	case IMX8QM_CLK_DUMMY:
+		return 0;
 	case IMX8QM_I2C0_IPG_CLK:
 	case IMX8QM_I2C0_CLK:
 	case IMX8QM_I2C0_DIV: