drm/mipi-dsi: Fix theoretical int overflow in mipi_dsi_dcs_write_seq()

The mipi_dsi_dcs_write_seq() macro makes a call to
mipi_dsi_dcs_write_buffer() which returns a type ssize_t. The macro
then stores it in an int and checks to see if it's negative. This
could theoretically be a problem if "ssize_t" is larger than "int".

To see the issue, imagine that "ssize_t" is 32-bits and "int" is
16-bits, you could see a problem if there was some code out there that
looked like:

  mipi_dsi_dcs_write_seq(dsi, cmd, <32767 bytes as arguments>);

...since we'd get back that 32768 bytes were transferred and 32768
stored in a 16-bit int would look negative.

Though there are no callsites where we'd actually hit this (even if
"int" was only 16-bit), it's cleaner to make the types match so let's
fix it.

Fixes: 2a9e9daf ("drm/mipi-dsi: Introduce mipi_dsi_dcs_write_seq macro")
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20240514102056.v5.1.I30fa4c8348ea316c886ef8a522a52fed617f930d@changeidSigned-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240514102056.v5.1.I30fa4c8348ea316c886ef8a522a52fed617f930d@changeid

include/drm/drm_mipi_dsi.h

@@ -333,18 +333,18 @@ int mipi_dsi_dcs_get_display_brightness_large(struct mipi_dsi_device *dsi,
  * @cmd: Command
  * @seq: buffer containing data to be transmitted
  */
-#define mipi_dsi_dcs_write_seq(dsi, cmd, seq...)                           \
-	do {                                                               \
-		static const u8 d[] = { cmd, seq };                        \
-		struct device *dev = &dsi->dev;                            \
-		int ret;                                                   \
-		ret = mipi_dsi_dcs_write_buffer(dsi, d, ARRAY_SIZE(d));    \
-		if (ret < 0) {                                             \
-			dev_err_ratelimited(                               \
-				dev, "sending command %#02x failed: %d\n", \
-				cmd, ret);                                 \
-			return ret;                                        \
-		}                                                          \
+#define mipi_dsi_dcs_write_seq(dsi, cmd, seq...)                            \
+	do {                                                                \
+		static const u8 d[] = { cmd, seq };                         \
+		struct device *dev = &dsi->dev;                             \
+		ssize_t ret;                                                \
+		ret = mipi_dsi_dcs_write_buffer(dsi, d, ARRAY_SIZE(d));     \
+		if (ret < 0) {                                              \
+			dev_err_ratelimited(                                \
+				dev, "sending command %#02x failed: %zd\n", \
+				cmd, ret);                                  \
+			return ret;                                         \
+		}                                                           \
 	} while (0)
 
 /**