[MOS] Fix signed bit shifts leading to out-of-bounds access

The event tracing code uses a const char array and bit shifts to convert byte
values (to be output into the trace) into two-character hex representation
through addressing the const array depending on the byte value. Since
char is signed, using char to represent byte values sometimes leads to
addressing an element of the const char array by a negative index. Replaced
with unsigned char.

media_driver/linux/common/os/mos_utilities_specific.c

@@ -2825,7 +2825,7 @@ void MOS_TraceEvent(
                 // convert raw event data to string. native raw data will be supported
                 // from linux kernel 4.10, hopefully we can skip this convert in the future.
                 const static char n2c[] = "0123456789ABCDEF";
-                char  *pData = (char *)pArg1;
+                unsigned char *pData = (unsigned char *)pArg1;
 
                 pTraceBuf[nLen++] = '|'; // prefix splite marker.
                 while(dwSize1-- > 0 && nLen < TRACE_EVENT_MAX_SIZE-2)
@@ -2835,7 +2835,7 @@ void MOS_TraceEvent(
                 }
                 if (pArg2)
                 {
-                    pData = (char *)pArg2;
+                    pData = (unsigned char *)pArg2;
                     while(dwSize2-- > 0 && nLen < TRACE_EVENT_MAX_SIZE-2)
                     {
                         pTraceBuf[nLen++] = n2c[(*pData) >> 4];