add function to convert access flags to legacy open mode

SMBLegacyOpen always opens a file as r/w. This could be problematic
for files with ATTR_READONLY set. Have it interpret the access_mode
into a sane open mode.

Signed-off-by: Steve French <sfrench@us.ibm.com>
diff --git a/fs/cifs/inode.c b/fs/cifs/inode.c
index fcbdbb6..2d53b43 100644
--- a/fs/cifs/inode.c
+++ b/fs/cifs/inode.c
@@ -1502,8 +1502,7 @@
 				int oplock = 0;
 
 				rc = SMBLegacyOpen(xid, pTcon, full_path,
-					FILE_OPEN,
-					SYNCHRONIZE | FILE_WRITE_ATTRIBUTES,
+					FILE_OPEN, GENERIC_WRITE,
 					CREATE_NOT_DIR, &netfid, &oplock,
 					NULL, cifs_sb->local_nls,
 					cifs_sb->mnt_cifs_flags &