db2_ldap: fix compilation warning

> ld_fld.c:831:19: warning: unused function 'db_double2ldap_str' [-Wunused-function]
> static inline int db_double2ldap_str(struct sbuf* buf, db_fld_t* fld)
>                   ^
> 1 warning generated.

(cherry picked from commit 5b1355aa3d9404a5165b0afbfdac384fe9cf785a)
(cherry picked from commit 91649cd46bf88d80f4fbcaccecb03e3a8fbae577)

src/modules/db2_ldap/ld_fld.c

@@ -828,7 +828,7 @@ static inline int db_float2ldap_str(struct sbuf* buf, db_fld_t* fld)
 }
 
 
-static inline int db_double2ldap_str(struct sbuf* buf, db_fld_t* fld)
+/*static inline int db_double2ldap_str(struct sbuf* buf, db_fld_t* fld)
 {
 	char tmp[16];
 	int len;
@@ -839,7 +839,7 @@ static inline int db_double2ldap_str(struct sbuf* buf, db_fld_t* fld)
 		return -1;
 	}
 	return sb_add(buf, tmp, len);
-}
+}*/
 
 static inline int ld_db2ldap(struct sbuf* buf, db_fld_t* fld) {
 	struct ld_fld* lfld;