Fix data buffer overrun and OLED corruption bug in oled_write_raw when cursor not at origin (0, 0)

[bcat]

Description

See #13203 for details on the bug itself. For simplicity, I updated oled_write_raw to follow the (non-buggy) pattern that oled_write_raw_P already uses for reads (incrementing the data pointer rather than indexing into it using array syntax).

Verified this fixes the display corruption bug for OLED on ARM. See before (with corruption) and after (without corruption) this fix.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

• Fixes [Bug] oled_write_raw overruns data buffer, corrupts display when cursor not at origin (0, 0) #13203.

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).