.gitignore: add *.su pattern

Ignore the *.su files generated by using the gcc option -fstack-usage.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Michal Marek <mmarek@suse.com>
diff --git a/.gitignore b/.gitignore
index 98b91fc..f0efae5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -36,6 +36,7 @@
 modules.builtin
 Module.symvers
 *.dwo
+*.su
 
 #
 # Top-level generic files