Try to inherit from website.layout_logo_show :

<template id="company_logo_show" inherit_id="website.layout_logo_show" customize_show="True" name="Show Logo">
    <xpath expr="//a[contains(@class, 'navbar-brand')]" position="replace">
        <a class="navbar-brand page-scroll logo" href="#page-top">
            <img src="/mf_theme/static/src/img/...."/>
        </a>
    </xpath>
</template>

@mahmoud:

<template id="layout_logo_show_my" inherit_id="website.layout_logo_show" customize_show="True" name="Show Logo">
        <xpath expr="//a[contains(@class, 'navbar-brand')]" position="replace">
            <a class="navbar-brand page-scroll logo" href="#page-top">
                <img src="/static/src/img/lg.png"/>
            </a>
        </xpath>
    </template>

its doesn't work to me? not error but for logo doesn't show in my website