Update usage of sprintf to use snprintf.

[NumericalPseudonym]

When building using default_envs = macOS in the platformio.ini file there are a number of build warnings like this:
'sprintf' is deprecated: This function is provided for compatibility reasons only. Due to security concerns inherent in the design of sprintf(3), it is highly recommended that you use snprintf(3) instead. [-Wdeprecated-declarations]

As discussed on the discord I've updated these using the snprintf([variableName], sizeof([variableName]), ..) pattern.

[KlausMu]

@NumericalPseudonym thanks for your PR.
To be complete, could you please also change it here:

OMOTE/Platformio/hardware/windows_linux/mqtt_hal_windows_linux.cpp

Line 132 in 38b6daf

sprintf(&buffer[i*3], "%02x:", (unsigned char) s.ifr_addr.sa_data[i]);