shader_buffers: fix macros and use in decode.

Pointed out by Gert on the mesa review.

src/virgl_protocol.h

@@ -496,8 +496,8 @@ enum virgl_context_cmd {
 #define VIRGL_SET_SHADER_BUFFER_SIZE(x) (VIRGL_SET_SHADER_BUFFER_ELEMENT_SIZE * (x)) + 2
 #define VIRGL_SET_SHADER_BUFFER_SHADER_TYPE 1
 #define VIRGL_SET_SHADER_BUFFER_START_SLOT 2
-#define VIRGL_SET_SHADER_BUFFER_OFFSET(x) ((x) * VIRGL_SET_SHADER_BUFFER_ELEMENT_SIZE + 2)
-#define VIRGL_SET_SHADER_BUFFER_LENGTH(x) ((x) * VIRGL_SET_SHADER_BUFFER_ELEMENT_SIZE + 3)
-#define VIRGL_SET_SHADER_BUFFER_RES_HANDLE(x) ((x) * VIRGL_SET_SHADER_BUFFER_ELEMENT_SIZE + 4)
+#define VIRGL_SET_SHADER_BUFFER_OFFSET(x) ((x) * VIRGL_SET_SHADER_BUFFER_ELEMENT_SIZE + 3)
+#define VIRGL_SET_SHADER_BUFFER_LENGTH(x) ((x) * VIRGL_SET_SHADER_BUFFER_ELEMENT_SIZE + 4)
+#define VIRGL_SET_SHADER_BUFFER_RES_HANDLE(x) ((x) * VIRGL_SET_SHADER_BUFFER_ELEMENT_SIZE + 5)
 
 #endif

src/vrend_decode.c

@@ -1097,9 +1097,9 @@ static int vrend_decode_set_shader_buffers(struct vrend_decode_ctx *ctx, uint16_
       return EINVAL;
 
    for (int i = 0; i < num_ssbo; i++) {
-      uint32_t offset = get_buf_entry(ctx, i * VIRGL_SET_SHADER_BUFFER_ELEMENT_SIZE + 3);
-      uint32_t buf_len = get_buf_entry(ctx, i * VIRGL_SET_SHADER_BUFFER_ELEMENT_SIZE + 4);
-      uint32_t handle = get_buf_entry(ctx, i * VIRGL_SET_SHADER_BUFFER_ELEMENT_SIZE + 5);
+      uint32_t offset = get_buf_entry(ctx, VIRGL_SET_SHADER_BUFFER_OFFSET(i));
+      uint32_t buf_len = get_buf_entry(ctx, VIRGL_SET_SHADER_BUFFER_LENGTH(i));
+      uint32_t handle = get_buf_entry(ctx, VIRGL_SET_SHADER_BUFFER_RES_HANDLE(i));
       vrend_set_single_ssbo(ctx->grctx, shader_type, start_slot + i, offset, buf_len,
                             handle);
    }