qemu-options: Add missing newline to -accel help text

The newline was removed by commit c97d6d2c, and broke -help output:

Before this patch:

  $ qemu-system-x86_64 -help | grep smp
                  thread=single|multi (enable multi-threaded TCG)-smp [...]

After this patch:

  $ qemu-system-x86_64 -help  | grep smp
  -smp [cpus=]n[,maxcpus=cpus][,cores=cores][,threads=threads][,sockets=sockets]

Fixes: c97d6d2c
Cc: Sergio Andres Gomez Del Real <sergio.g.delreal@gmail.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Message-Id: <20180611195607.3015-1-ehabkost@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

qemu-options.hx

@@ -130,7 +130,7 @@ ETEXI
 DEF("accel", HAS_ARG, QEMU_OPTION_accel,
     "-accel [accel=]accelerator[,thread=single|multi]\n"
     "                select accelerator (kvm, xen, hax, hvf, whpx or tcg; use 'help' for a list)\n"
-    "                thread=single|multi (enable multi-threaded TCG)", QEMU_ARCH_ALL)
+    "                thread=single|multi (enable multi-threaded TCG)\n", QEMU_ARCH_ALL)
 STEXI
 @item -accel @var{name}[,prop=@var{value}[,...]]
 @findex -accel