vmw_balloon: fix for a -Wuninitialized warning

vmw_balloon: fix for a -Wuninitialized warning

commit 3e5ba466d515eb3fb1e0e975a3d8e499126ae2b5 upstream.

Fix for a -Wuninitialized compiler warning. Changed return value of
vmballoon_send_lock_page() from bool to int to be able to distinguish
between the error cases to avoid uninitialized use of hv_status in
vmballoon_reserve_page()

Signed-off-by: Danny Kukawka <danny.kukawka@bisect.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>