drm: meson: fix address type confusion

Casting a pointer to dma_addr_t produces a warning:

drivers/gpu/drm/meson/meson_rdma.c: In function 'meson_rdma_free':
drivers/gpu/drm/meson/meson_rdma.c:59:25: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
  priv->rdma.addr_phys = (dma_addr_t)NULL;

In this case, it's worse because the variable name has the suffix
'_phys', which often indicates a phys_addr_t rather than dma_addr_t,
i.e. yet another incompatible type.

Change it to use consistent naming and avoid NULL.

Fixes: 63fba242 ("drm/meson: add RDMA module driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200107214653.1173199-1-arnd@arndb.de

drivers/gpu/drm/meson/meson_drv.h

@@ -135,7 +135,7 @@ struct meson_drm {
 	} venc;
 
 	struct {
-		dma_addr_t addr_phys;
+		dma_addr_t addr_dma;
 		uint32_t *addr;
 		unsigned int offset;
 	} rdma;

drivers/gpu/drm/meson/meson_rdma.c

@@ -27,7 +27,7 @@ int meson_rdma_init(struct meson_drm *priv)
 		/* Allocate a PAGE buffer */
 		priv->rdma.addr =
 			dma_alloc_coherent(priv->dev, SZ_4K,
-					   &priv->rdma.addr_phys,
+					   &priv->rdma.addr_dma,
 					   GFP_KERNEL);
 		if (!priv->rdma.addr)
 			return -ENOMEM;
@@ -47,16 +47,16 @@ int meson_rdma_init(struct meson_drm *priv)
 
 void meson_rdma_free(struct meson_drm *priv)
 {
-	if (!priv->rdma.addr && !priv->rdma.addr_phys)
+	if (!priv->rdma.addr && !priv->rdma.addr_dma)
 		return;
 
 	meson_rdma_stop(priv);
 
 	dma_free_coherent(priv->dev, SZ_4K,
-			  priv->rdma.addr, priv->rdma.addr_phys);
+			  priv->rdma.addr, priv->rdma.addr_dma);
 
 	priv->rdma.addr = NULL;
-	priv->rdma.addr_phys = (dma_addr_t)NULL;
+	priv->rdma.addr_dma = (dma_addr_t)0;
 }
 
 void meson_rdma_setup(struct meson_drm *priv)
@@ -118,11 +118,11 @@ void meson_rdma_flush(struct meson_drm *priv)
 	meson_rdma_stop(priv);
 
 	/* Start of Channel 1 register writes buffer */
-	writel(priv->rdma.addr_phys,
+	writel(priv->rdma.addr_dma,
 	       priv->io_base + _REG(RDMA_AHB_START_ADDR_1));
 
 	/* Last byte on Channel 1 register writes buffer */
-	writel(priv->rdma.addr_phys + (priv->rdma.offset * RDMA_DESC_SIZE) - 1,
+	writel(priv->rdma.addr_dma + (priv->rdma.offset * RDMA_DESC_SIZE) - 1,
 	       priv->io_base + _REG(RDMA_AHB_END_ADDR_1));
 
 	/* Trigger Channel 1 on VSYNC event */