A11Y nitpick: correct mnemonic widget mapping

This warning appeared while opening the 4th page of Mail Merge Wizard

warn:vcl:5291:1:vcl/source/window/builder.cxx:220: missing either source
 femalecolft or target fieldname member of Mnemonic Widget Mapping
warn:vcl:5291:1:vcl/source/window/builder.cxx:220: missing either source
femalefieldft or target fieldvalue member of Mnemonic Widget Mapping

Change-Id: Ibde465ab1a3603a6b4f831e8d7939b512c4b593e
Reviewed-on: https://gerrit.libreoffice.org/34934
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>
diff --git a/sw/uiconfig/swriter/ui/mmsalutationpage.ui b/sw/uiconfig/swriter/ui/mmsalutationpage.ui
index 0ad0e93..265438b 100644
--- a/sw/uiconfig/swriter/ui/mmsalutationpage.ui
+++ b/sw/uiconfig/swriter/ui/mmsalutationpage.ui
@@ -311,7 +311,7 @@
                                            <property name="xalign">0</property>
                                            <property name="label" translatable="yes">Field name</property>
                                            <property name="use_underline">True</property>
                                            <property name="mnemonic_widget">fieldname</property>
                                            <property name="mnemonic_widget">femalecol</property>
                                          </object>
                                          <packing>
                                            <property name="left_attach">0</property>
@@ -327,7 +327,7 @@
                                            <property name="xalign">0</property>
                                            <property name="label" translatable="yes">Field value</property>
                                            <property name="use_underline">True</property>
                                            <property name="mnemonic_widget">fieldvalue</property>
                                            <property name="mnemonic_widget">femalefield</property>
                                          </object>
                                          <packing>
                                            <property name="left_attach">0</property>