staging: csr: remove casting of return value from kmalloc

as per Documentation/CodingStyle, casting of void pointer to
any other pointer is not needed

Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Acked-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>