staging: flexfb: Remove initialization to 0

(the initial post had a typo in the short summary, reposting)

This fixes some of the code style issues in the flexfb driver by removing
unnecessary initializations of static variables to 0 or to NULL.

Signed-off-by: Mauro Stettler <mauro.stettler@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Noralf Tronnes <notro@tronnes.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>