[CIFS] Remove sparse warning

Move extern for cifsConvertToUCS to different header to prevent following warning:

CHECK   fs/cifs/cifs_unicode.c
fs/cifs/cifs_unicode.c:267:1: warning: symbol 'cifsConvertToUCS' was not declared. Should it be static?

Signed-off-by: Steve French <sfrench@us.ibm.com>
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <sfrench@us.ibm.com>
diff --git a/fs/cifs/cifs_unicode.h b/fs/cifs/cifs_unicode.h
index 644dd882..6d02fd5 100644
--- a/fs/cifs/cifs_unicode.h
+++ b/fs/cifs/cifs_unicode.h
@@ -82,6 +82,9 @@
 char *cifs_strndup_from_ucs(const char *src, const int maxlen,
 			    const bool is_unicode,
 			    const struct nls_table *codepage);
+extern int cifsConvertToUCS(__le16 *target, const char *source, int maxlen,
+			const struct nls_table *cp, int mapChars);
+
 #endif
 
 /*