wifi: ath12k: Fix for out-of bound access error

In the Linux kernel, the following vulnerability has been resolved: wifi: ath12k: Fix for out-of bound access error Selfgen stats are placed in a buffer using print_array_to_buf_index() function. Array length parameter passed to the function is too big, resulting in possible out-of bound memory error. Decreasing buffer size by one fixes faulty upper bound of passed array. Discovered in coverity scan, CID 1600742 and CID 1600758