Fix schema correctness for element 'share'

jing would say:
samba-server.rng:2249:27: error: a group of attributes must not be repeatable
(section 7.1 of the RELAX NG specification requires that the simplified XML
form of the schema not contain any elements matching the path
oneOrMore//group//attribute)

This part of the schema looks fishy (as do other parts) but let's just get
over the correctness part now.

src/autoyast-rnc/samba-server.rnc

@@ -484,6 +484,6 @@ samba_options = element options {
   MAP,
   element option { MAP, samba_option_key, samba_option_val? }*
 }
-share = element share { (STRING | y2_share)* }
+share = element share { (text | y2_share)* }
 samba_option_key = element key { STRING }
 samba_option_val = element value { STRING }