[FIX] web: properly apply css in mobile search view

In some cases, if the device is in a mobile mode, but does not support
touch, then the mobile search view is shown, as expected, but the css
is not applied.

Maybe this is not a big deal in practice, since the only way to notice this is
to use odoo on a browser with a small window and no touch emulation, but
this is still annoying and wrong: if the mobile search view is
displayed, the its css should be applied in all cases.

We simply fix the css rule to make it work like expected.