`BP_Activity_Query::get_sql_for_clause()` can wrongly use `$wpdb->prepare()`

[imath]

I wasn't able to find which part of the code is trying to query activities comparing hide_sitewide to [ 0, 1 ], but this is causing a doing it wrong notice with $wpdb->prepare().

To avoid it, I believe we simply need to make sure the placeholder used with $wpdb->prepare() is an integer as expected.

I'll suggest a PR asap.

Avoid wrong usage of $wpdb->prepare() in BP_Activity_Query::get_sql_for_clause()

Trac ticket: ​https://buddypress.trac.wordpress.org/ticket/9017

[imath]

In 13634:

Avoid $wpdb->prepare() wrong usage when getting favorited activities

In the BP_Activity_Query::get_sql_for_clause() method, make sure the placeholder used with $wpdb->prepare() is an integer as expected when setting the hide_sitewide clause.

Fixes #9017
Closes ​https://github.com/buddypress/buddypress/pull/186