staging: mt29f_spinand: remove pointer to pointer cast in function argument

Removes unnecessary pointer to pointer cast on function arguments.
It is worth noting that buf is already a u8 pointer.
Issue detected and resolved using the following coccinelle script:

@@
expression e;
type t;
identifier f;
@@

f(...,
-(t *)
e
,...)

Signed-off-by: Aya Mahfouz <mahfouz.saif.elyazal@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>