Show meaningful message when Trezor is not connected

[srirambv]

Description

Show meaningful message when Trezor is not connected

Steps to Reproduce

1. Connect Trezor and go to add account
2. Click on Trezor to make the popup tab to show up to export private keys
3. Close the popup tab and go back to wallet, shows error which doesn't make sense

Actual result:

Expected result:

Show meaningful message for errors

Reproduces how often:

Easy

Brave version (brave://version info)

Brave	1.32.95 Chromium: 95.0.4638.69 (Official Build) beta (64-bit)
Revision	6a1600ed572fedecd573b6c2b90a22fe6392a410-refs/branch-heads/4638@{#984}
OS	All

Version/Channel Information:

• Can you reproduce this issue with the current release? NA
• Can you reproduce this issue with the beta channel? Yes
• Can you reproduce this issue with the nightly channel? Yes

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? NA
• Does the issue resolve itself when disabling Brave Rewards? NA
• Is the issue reproducible on the latest version of Chrome? NA

Miscellaneous Information:

cc; @jamesmudgett @spylogsster

[srirambv]

Brave	1.34.77 Chromium: 97.0.4692.56 (Official Build) (64-bit)
Revision	04da6c66398ca50e603cc236a07dc7dfd3bbc750-refs/branch-heads/4692@{#990}
OS	☑️ Linux	☑️ Windows 11 Version Dev (Build 22523.1000)	☑️ macOS Version 12.0.1 (Build 21A559)
Verified steps from issue description Verified error message is updated. Confirmed with @spylogsster about the updated message