drivers/misc: at25: convert to use devm_kzalloc

Use devm_kzalloc to make cleanup paths simpler

Signed-off-by: Nikolay Balandin <nbalandin@dev.rtsoft.ru>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>