ANDROID: fix build warning in mokvar-table.c

In commit 46c0454f ("efi: Don't map the entire mokvar table to
determine its size"), a build warning is added which breaks the Android
build which treats all warnings as errors.  So fix it up.

Fixes: 46c0454f ("efi: Don't map the entire mokvar table to determine its size")
Change-Id: I1f13f2aac99242cda34f10f43cb14aa9300287f1
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>