arm: mach-k3: am62p: annotate switch/case fallthrough

The MMC boot mode selection for the TI AM62P series of SoCs uses an
implicit switch/case fallthrough for falling back to some default
boot mode.

Add our "fallthrough;" statement-like macro before the default branch in
the code, to avoid a warning when GCC's -Wimplicit-fallthrough warning
option is enabled.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/mach-k3/am62px/am62p5_init.c b/arch/arm/mach-k3/am62px/am62p5_init.c
index 14a46fa..01e47de 100644
--- a/arch/arm/mach-k3/am62px/am62p5_init.c
+++ b/arch/arm/mach-k3/am62px/am62p5_init.c
@@ -266,6 +266,7 @@
 	case BOOT_DEVICE_MMC:
 		if (bootmode_cfg & MAIN_DEVSTAT_PRIMARY_MMC_FS_RAW_MASK)
 			return MMCSD_MODE_RAW;
+		fallthrough;
 	default:
 		return MMCSD_MODE_FS;
 	}