staging: wlags49: don't use custom implementation of atoi()

Kernel has its own method called simple_strtoul() to do such things.

Here we are using simple_strtoul(value, NULL, 0) because in original function
the recognized base is 10 or 16 and input data is assumed to be unsigned.

Signed-off-by: Andy Shevchenko <ext-andriy.shevchenko@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>