clang-format: Enable InsertBraces option

Zephyr's coding guidelines require braces on every code block body.
Enable InsertBraces option so clang-format automatically adds these
braces.

Signed-off-by: Keith Short <keithshort@google.com>
diff --git a/.clang-format b/.clang-format
index d68699c..03aca80 100644
--- a/.clang-format
+++ b/.clang-format
@@ -77,6 +77,7 @@
     Priority: 3
 IndentCaseLabels: false
 IndentWidth: 8
+InsertBraces: true
 # SpaceBeforeParens: ControlStatementsExceptControlMacros # clang-format >= 13.0
 SortIncludes: false
 UseTab: Always