Fix this sparse warnings:
  drivers/ide/ide-disk_proc.c:130:11: warning: Using plain integer as NULL pointer
  drivers/ide/ide-floppy_proc.c:32:11: warning: Using plain integer as NULL pointer
  drivers/ide/ide-proc.c:234:11: warning: Using plain integer as NULL pointer
  drivers/ide/ide-tape.c:2141:11: warning: Using plain integer as NULL pointer

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Cc: trivial@kernel.org
Cc: kernel-janitors@vger.kernel.org
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>