grub2: fix compile error with glibc 2.19.1

BUG=chromium:400426
TEST=grub compiles with glibc 2.19.1

Change-Id: Icef6829461ab037f356b66720f788617ac165da1
Reviewed-on: https://chromium-review.googlesource.com/211001
Reviewed-by: Mike Frysinger <[email protected]>
Commit-Queue: Yunlian Jiang <[email protected]>
Tested-by: Yunlian Jiang <[email protected]>
1 file changed