eeprom: idt_89hpesx: remove unneeded csr_file variable

The csr_file variable was only ever set, never read.  So remove it from
struct idt_89hpesx_dev as it is pointless to keep around.

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Colin Ian King <colin.king@canonical.com>
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>