ANDROID: GKI: 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, but Android kernels are
built to not allow any warnings, so fix this up.

Fixes: 46c0454f ("efi: Don't map the entire mokvar table to determine its size")
Change-Id: I84b5bd4a184bd24b267c0abb2f9347cd9f7a1a5d
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>