kobject: Use return value of strreplace()

Since strreplace() returns the pointer to the string itself,
we may use it directly in the code.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230605170553.7835-4-andriy.shevchenko@linux.intel.com