windows: Don't panic if driver not installed

[JohnAZoidberg]

Trying it out without running as admin to cause it to fail accessing the driver.

# After
> cargo run --no-default-features --features "windows" -p framework_tool -- --test
Self-Test
  SMBIOS Platform:     Framework13AmdAi300
  Dump EC memory region
[ERROR] Failed to find Windows driver. Error { code: HRESULT(0x80070005), message: "Access is denied." }
[ERROR] Failed to communicate with EC. Reason: "Failed to initialize"
    Failed to read EC memory region
FAILED!!
Error: "Fail"
error: process didn't exit successfully: `target\debug\framework_tool.exe --test` (exit code: 1)

# Before
> cargo run --no-default-features --features "windows" -p framework_tool -- --test
Self-Test
  SMBIOS Platform:     Framework13AmdAi300
  Dump EC memory region
thread 'main' panicked at framework_lib\src\chromium_ec\windows.rs:46:14:
called `Result::unwrap()` on an `Err` value: Error { code: HRESULT(0x80070005), message: "Access is denied." }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
error: process didn't exit successfully: `target\debug\framework_tool.exe --test` (exit code: 101)