Remove volatile compound assignments and add cast for min

[caternuson]

Removes use of compound assignments with volatiles to avoid compile warns. Example warn for ref:

  /home/runner/Arduino/libraries/Adafruit_EPD/src/Adafruit_EPD.cpp:659:11: warning: compound assignment with 'volatile'-qualified left operand is deprecated [-Wvolatile]
    659 |   *csPort |= csPinMask;
        |   ~~~~~~~~^~~~~~~~~~~~

Also adds an explicit cast to a min call that was causing a compile error:

  /home/runner/Arduino/libraries/Adafruit_EPD/src/drivers/Adafruit_ACeP.cpp:132:28: error: no matching function for call to 'min(uint32_t&, unsigned int)'
    132 |     uint32_t numbytes = min(remaining, sizeof(block));
        |                         ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~

[caternuson]

Tested with a Feather ESP32 and an old model PID 3625 EPD running library example: https://github.com/adafruit/Adafruit_EPD/blob/master/examples/ThinkInk_tricolor/ThinkInk_tricolor.ino

[caternuson]

@ladyada for review

[ladyada]

looks great thanks!