platform/x86: GPD pocket fan: fix spelling mistake: "Mill-celcius" -> "millicelsius"

Trivial fix to spelling mistake in MODULE_PARM_DESC text and remove
unnecessary hyphen.

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