libdrm/radeon: Fix section size mismatch to reset the section.

If there is section size mismatch reusing the section object
makes section start fail.
Reseting the object before doing error checking prevents the
possible flood of errors.
diff --git a/radeon/radeon_cs_gem.c b/radeon/radeon_cs_gem.c
index c2301ad..45a219c 100644
--- a/radeon/radeon_cs_gem.c
+++ b/radeon/radeon_cs_gem.c
@@ -260,7 +260,10 @@
                 cs->section_file, cs->section_func, cs->section_line, cs->section_ndw, cs->section_cdw);
         fprintf(stderr, "CS section end at (%s,%s,%d)\n",
                 file, func, line);
-        return -EPIPE;
+
+	/* We must reset the section even when there is error. */
+	cs->section_ndw = 0;
+	return -EPIPE;
     }
     cs->section_ndw = 0;
     return 0;