gfs2: make timeout values more explicit

'timeout' is a vague name for the return value of wait_event_*_timeout
because it actually returns the time left. Because the variable is never
used later, just drop the return value. Since variable 'timeout' is then
only used to carry a fixed timeout value, drop this in favor of a fixed
function argument as in the other call to wait_event_timeout() above.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>