Incorrect mstatus Setting for Non-Existent CSR Access in M-Mode

[youzi27]

Describe the bug

When accessing a specific non-existent CSR (e.g., 0xb7d) in M-mode, NutShell sets the mstatus register incorrectly, while other CSRs such as mepc and mcause remain consistent with Spike. Upon reviewing the NutShell source code CSR, there is no evidence of a custom implementation for this CSR.

Steps to Reproduce

1. Enter M-mode.
2. Attempt to access a non-existent CSR, such as 0xb7d.
3. Compare the behavior of NutShell's CSRs.

Screenshots