ui/gtk: don't try to redefine SI prefixes

Redefining SI prefixes is always wrong. 1s has per definition
1000ms. Remove the misnamed named constant and replace it with
a comment explaining the frequency to period conversion in two
simple steps. Now you can cancel out the unit mHz in the comment
with the implicit unit mHz in refresh_rate_millihz and see why
the implicit unit ms for update_interval remains.

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Message-Id: <20201213165724.13418-1-vr_qemu@t-online.de>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

include/ui/gtk.h

@@ -24,8 +24,6 @@
 #include "ui/egl-context.h"
 #endif
 
-#define MILLISEC_PER_SEC 1000000
-
 typedef struct GtkDisplayState GtkDisplayState;
 
 typedef struct VirtualGfxConsole {

ui/gtk.c

@@ -798,7 +798,8 @@ static gboolean gd_draw_event(GtkWidget *widget, cairo_t *cr, void *opaque)
     refresh_rate_millihz = gd_refresh_rate_millihz(vc->window ?
                                                    vc->window : s->window);
     if (refresh_rate_millihz) {
-        vc->gfx.dcl.update_interval = MILLISEC_PER_SEC / refresh_rate_millihz;
+        /* T = 1 / f = 1 [s*Hz] / f = 1000*1000 [ms*mHz] / f */
+        vc->gfx.dcl.update_interval = 1000 * 1000 / refresh_rate_millihz;
     }
 
     fbw = surface_width(vc->gfx.ds);