MIPS: Alchemy: Correct code taking the size of a pointer

sizeof(dp) is just the size of the pointer.  Change it to the size of the
referenced structure.

A simplified version of the semantic patch that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@@
expression *x;
expression f;
type T;
@@

*f(...,(T)x,...)
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Patchwork: http://patchwork.linux-mips.org/patch/789/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>