mfd: intel-lpss: Correct names of RESETS register bits

According to documentation the function has 2 bits for reset
while iDMA 64-bit has only one.

Rename it accordingly. Note, there is no functional change since
we always handle them together.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>