um: Add missing trailing newline to help messages

Some help messages are missing a trailing newline. They should
end with two newlines, but only one is present. Add the missing
newline to make the --help output more readable.

Signed-off-by: Tiwei Bie <[e-mail]>
Signed-off-by: Johannes Berg <[e-mail]>

arch/um/drivers/ubd_kern.c

···
 "    useful when a unique number should be given to the device. Note when\n"
 "    specifying a label, the filename2 must be also presented. It can be\n"
 "    an empty string, in which case the backing file is not used:\n"
-"       ubd0=File,,Serial\n"
+"       ubd0=File,,Serial\n\n"
 );
 
 static int udb_setup(char *str)

arch/um/kernel/dtb.c

···
 
 __uml_setup("dtb=", uml_dtb_setup,
 "dtb=<file>\n"
-"    Boot the kernel with the devicetree blob from the specified file.\n"
+"    Boot the kernel with the devicetree blob from the specified file.\n\n"
 );

arch/um/kernel/time.c

···
 "have more than one system simultaneously be on simulated time. The virtio\n"
 "driver code in UML knows about this so you can also simulate networks and\n"
 "devices using it, assuming the device has the right capabilities.\n"
-"The optional ID is a 64-bit integer that's sent to the central scheduler.\n");
+"The optional ID is a 64-bit integer that's sent to the central scheduler.\n\n");
 
 static int setup_time_travel_start(char *str)
 {
···
 __uml_help(setup_time_travel_start,
 "time-travel-start=<nanoseconds>\n"
 "Configure the UML instance's wall clock to start at this value rather than\n"
-"the host's wall clock at the time of UML boot.\n");
+"the host's wall clock at the time of UML boot.\n\n");
+
 static struct kobject *bc_time_kobject;
 
 static ssize_t bc_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)

arch/um/os-Linux/skas/process.c

···
 "noreboot\n"
 "    Rather than rebooting, exit always, akin to QEMU's -no-reboot option.\n"
 "    This is useful if you're using CONFIG_PANIC_TIMEOUT in order to catch\n"
-"    crashes in CI\n");
+"    crashes in CI\n\n");
 
 void reboot_skas(void)
 {