Small tweaks allows running on ATMega2560

[ClutchplateDude]

Describe the bug
The library does not compile out of the box for an Arduino ATMega2560 board (or any other 8-bit board)

To Reproduce
Steps to reproduce the behavior:

1. Open Sketch
2. Set Board to and Arduino Mega2560
3. Compile
4. _frequency overflow

Expected behavior
Would be great to be able to use this library on a Arduino 8-bit board (almost there)

Versions (please complete the following information):

• Library: 4.4.1
• Platform: Arduino atmelavr@4.2.0

Additional context
If the type of the _frequency variable of the SSD1306Wire class is changed from int to long, it will work.
Also, using PlatformIO, I get compiler warnings about ctor parameters shadowing members. If you remove the leading underscores from the ctor parameters, it goes away.

[ClutchplateDude]

I have tested this on our project that can be built for Mega2560 and ESP32 and the library works on both platforms with this tweak. I will open a PR for this shortly.