platform/x86: intel_ips: remove redundant variables slope and offset

Variables slope and offset are being assigned but are never used hence
they are redundant and can be removed.

Cleans up clang warnings:
warning: variable 'slope' set but not used [-Wunused-but-set-variable]
warning: variable 'offset' set but not used [-Wunused-but-set-variable]

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>