eficonfig: set EFICONFIG_ENTRY_NUM_MAX to INT_MAX - 1

eficonfig_append_menu_entryi() accepts the number of entries
less than or equal to EFICONFIG_ENTRY_NUM_MAX.
EFICONFIG_ENTRY_NUM_MAX is currently set as INT_MAX, so
the invalid menu count check(efi_menu->count > EFICONFIG_ENTRY_NUM_MAX)
in eficonfig_process_common() is always false.

This commit sets EFICONFIG_ENTRY_NUM_MAX to (INT_MAX - 1).

Reported-by: Coverity (CID 435659)
Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>