efi_loader: always check parameters in efi_cout_query_mode()

If we cannot determine the size of the serial terminal we still have
to check the parameters of efi_cout_query_mode().

Querying the size of the serial terminal drains the keyboard buffer.
So make sure we do this during the initialization and not in the midst
of an EFI application.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>