mbrola: Specify more the spanish voices

This specifies that the es* mbrola voices are rather for Spanish
spanish.

espeak-ng-data/voices/mb/mb-es1

@@ -1,3 +1,4 @@
+language es-es 7
 language es 7
 name spanish-mbrola-1
 gender male

espeak-ng-data/voices/mb/mb-es2

@@ -1,3 +1,4 @@
+language es-es 7
 language es 7
 name spanish-mbrola-2
 gender male

espeak-ng-data/voices/mb/mb-es3

@@ -1,3 +1,4 @@
+language es-es 3
 language es 3
 name spanish-mbrola-3
 gender female

espeak-ng-data/voices/mb/mb-es4

@@ -1,3 +1,4 @@
+language es-es 4
 language es 4
 name spanish-mbrola-4
 gender male