migration/multifd: Fix compile error caused by page_size usage

migration/multifd: Fix compile error caused by page_size usage

>From Commit 90fa121c6c07 ("migration/multifd: Inline page_size and
page_count") onwards page_size is not part of MutiFD*Params but uses
an inline constant instead.

However, it missed updating an old usage, causing a compile error.

Fixes: 90fa121c6c07 ("migration/multifd: Inline page_size and page_count")
Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-Id: <20241203124943.52572-1-shameerali.kolothum.thodi@huawei.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
(cherry picked from commit d127294f265e6a17f8d614f2bef7df8455e81f56)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>