gdrom: Fix compile error

Return value and argument of block_device_operations.release of gdrom
was changed.
This patch fix this problem.

Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>