freedreno: Check file descriptor before write.

Fix defect reported by Coverity Scan.

Argument cannot be negative (NEGATIVE_RETURNS)
negative_returns: fd is passed to a parameter that cannot be
negative.

Fixes: 1ea4ef0d3b ("freedreno: slurp in decode tools")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6696>

src/freedreno/decode/cffdec.c

@@ -403,8 +403,10 @@ dump_shader(const char *ext, void *buf, int bufsz)
 		int fd;
 		sprintf(filename, "%04d.%s", n++, ext);
 		fd = open(filename, O_WRONLY| O_TRUNC | O_CREAT, 0644);
-		write(fd, buf, bufsz);
-		close(fd);
+		if (fd != -1) {
+			write(fd, buf, bufsz);
+			close(fd);
+		}
 	}
 }