MdeModulePkg/BootMaintenanceManagerUiLib: rebase to ARRAY_SIZE()

MdeModulePkg/BootMaintenanceManagerUiLib: rebase to ARRAY_SIZE()

Cc: Dandan Bi <dandan.bi@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Feng Tian <feng.tian@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Feng Tian <feng.tian@Intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>