EDAC, pnd2: Correct misleading error message in mk_region_mask()

The mask parameter is expected to be of a sequence of the set bits.
It does not mean it must be power of two (only single bit set).
Correct misleading error message.

Suggested-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>