Adjust gitignore for /build

/build-* can't ignore /build.

Signed-off-by: Rong Tao <rongtao@cestc.cn>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/.gitignore b/.gitignore
index 002f95d..9697f00 100644
--- a/.gitignore
+++ b/.gitignore
@@ -35,7 +35,7 @@
 *.tab.[ch]
 
 # Build tree
-/build-*
+/build*
 
 #
 # Top-level generic files