vt6655: balance faulty parentheses in 80211hdr.h

The file 80211hdr.h contained the macro WLAN_GET_FC_PRVER(n). The big endian
fashion of this macro had unbalanced parentheses. This patch removes the
parentheses in question.

Signed-off-by: Martin Hofmann <martin.hofmann@studium.uni-erlangen.de>
Signed-off-by: Michael Gunselmann <michael.gunselmann@studium.uni-erlangen.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>