ACPI: sbshc: Fix fall-through warning for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix a
fallthrough warning by simply dropping the empty default case at
the bottom.

This contributes to the ongoing efforts to globally enable
-Wimplicit-fallthrough for Clang.

Link: https://github.com/KSPP/linux/issues/115
Suggested-by: Rafael J. Wysocki <[e-mail]>
Link: https://lore.kernel.org/lkml/[e-mail]/
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/acpi/sbshc.c

···
 		case ACPI_SBS_BATTERY:
 			acpi_os_execute(OSL_NOTIFY_HANDLER,
 					acpi_smbus_callback, hc);
-		default:;
 	}
 	mutex_unlock(&hc->lock);
 	return 0;