drivers/staging/rtl8187se: Don't pass huge struct by value

struct ieee80211_network is fairly large (more than half a kilobyte),
so let's pass a pointer instead of passing the entire structure by
value when ieee80211_is_54g() and ieee80211_is_shortslot() need to
look at a few members.
Also remove parentheses around the values being returned from those
two functions - 'return' is not a function.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>