[CIFS] Fix memory overwrite when saving nativeFileSystem field during mount

CIFS can allocate a few bytes to little for the nativeFileSystem field
during tree connect response processing during mount.  This can result
in a "Redzone overwritten" message to be logged.

Signed-off-by: Sridhar Vinay <vinaysridhar@in.ibm.com>
Acked-by: Shirish Pargaonkar <shirishp@us.ibm.com>
CC: Stable <stable@kernel.org>
Signed-off-by: Steve French <sfrench@us.ibm.com>