Bump version for 2.4.75 release

For Intel explicit fencing.

Signed-off-by: Chad Versace <chadversary@chromium.org>
diff --git a/configure.ac b/configure.ac
index 39973b6..8e59332 100644
--- a/configure.ac
+++ b/configure.ac
@@ -20,7 +20,7 @@
 
 AC_PREREQ([2.63])
 AC_INIT([libdrm],
-        [2.4.74],
+        [2.4.75],
         [https://bugs.freedesktop.org/enter_bug.cgi?product=DRI],
         [libdrm])