travis: Enable coverity.
tracker: coverity fix for chsnprintf returning -1
cmd: coverity: Fix Out-of-bounds bug.
nmea: coverity: Add NULL pointer check.
gsm: coverity: Fix using NULL pointer.
tracker: coverity: Fix use of strncpy.
gsm: coverity: Fix use of strncpy.
uart: coverity: Fix check for SC_UART_LAST.