qemu-options: replace constant 1 with HAS_ARG

This is the only instance of a non-zero constant not using a symbolic
constant.
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20200204165638.25051-1-jsnow@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

qemu-options.hx

@@ -1955,7 +1955,7 @@ STEXI
 Start in full screen.
 ETEXI
 
-DEF("g", 1, QEMU_OPTION_g ,
+DEF("g", HAS_ARG, QEMU_OPTION_g ,
     "-g WxH[xDEPTH]  Set the initial graphical resolution and depth\n",
     QEMU_ARCH_PPC | QEMU_ARCH_SPARC | QEMU_ARCH_M68K)
 STEXI