[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>

fs/cifs/cifs_unicode.h

@@ -82,6 +82,9 @@ int cifs_strtoUCS(__le16 *, const char *, int, const struct nls_table *);
 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
 
 /*

fs/cifs/cifsproto.h

@@ -353,8 +353,6 @@ extern int CIFSGetSrvInodeNumber(const int xid, struct cifsTconInfo *tcon,
 			const unsigned char *searchName, __u64 *inode_number,
 			const struct nls_table *nls_codepage,
 			int remap_special_chars);
-extern int cifsConvertToUCS(__le16 *target, const char *source, int maxlen,
-			const struct nls_table *cp, int mapChars);
 
 extern int CIFSSMBLock(const int xid, struct cifsTconInfo *tcon,
 			const __u16 netfid, const __u64 len,