[simple-scan] Fix a warning

[Bartosz <bkosiorek src gnome org>]

commit 5e4f5329e252399280a3ad7a0a35ca0bc8fc6f81
Author: Sabri Ünal <libreajans gmail com>
Date:   Sat Dec 28 11:02:46 2019 +0000

    Fix a warning
    
    Gtk-WARNING: widget 'GtkBox' isn't suitable for mnemonic activation

 src/preferences-dialog.ui | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/preferences-dialog.ui b/src/preferences-dialog.ui
index de791cb..b4a256c 100644
--- a/src/preferences-dialog.ui
+++ b/src/preferences-dialog.ui
@@ -300,7 +300,7 @@
                     <child>
                       <object class="GtkLabel" id="text_dpi_label">
                         <property name="visible">True</property>
-                        <property name="label" translatable="yes" comments="Label beside scan source combo 
box">_Text Resolution</property>
+                        <property name="label" translatable="yes" comments="Label beside scan source combo 
box">Text Resolution</property>
                         <property name="use_underline">True</property>
                         <property name="xalign">1</property>
                         <style>
@@ -315,7 +315,7 @@
                     <child>
                       <object class="GtkLabel" id="photo_dpi_label">
                         <property name="visible">True</property>
-                        <property name="label" translatable="yes" comments="Label beside scan source combo 
box">_Photo Resolution</property>
+                        <property name="label" translatable="yes" comments="Label beside scan source combo 
box">Photo Resolution</property>
                         <property name="use_underline">True</property>
                         <property name="xalign">1</property>
                         <style>