at25: fix debug and error messaging

The patch does the following:
- fixes specifiers and removes explicit casting of the parameters
- joins literals to one line
- increases readability of the parameters

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>