cifs: don't use __constant_cpu_to_le32()

A trivial patch.

cpu_to_le32() is capable enough to detect __builtin_constant_p()
and to use an appropriate compile time ___constant_swahb32()
function.

So we can use cpu_to_le32() instead of __constant_cpu_to_le32().
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Steve French <stfrench@microsoft.com>