powerpc/spufs: Fix incorrect buffer offset in regs write

We need to offset by *pos bytes, not *pos words.
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/cell/spufs/file.c

@@ -578,7 +578,7 @@ spufs_regs_write(struct file *file, const char __user *buffer,
 	if (ret)
 		return ret;
 
-	ret = copy_from_user(lscsa->gprs + *pos - size,
+	ret = copy_from_user((char *)lscsa->gprs + *pos - size,
 			     buffer, size) ? -EFAULT : size;
 
 	spu_release_saved(ctx);