Staging: xgifb: increase VBIOS_VER_MAX_LENGTH to 5

VBIOS_VER_MAX_LENGTH was set to 4, but the value "0.84" is strcpy'd
into it.  That value is 5 long including the trailing NULL.

Signed-off-by: Bill Pemberton <wfp5p@virginia.edu>
Cc: Arnaud Patard <apatard@mandriva.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>