libphoenix: fix mutexing in pthread_create

[adamdebek]

RTOS-651

Description

Motivation and Context

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

How Has This Been Tested?

• Already covered by automatic testing.
• New test added: (add PR link here).
• Tested by hand on: (list targets here).

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing linter checks and tests passed.
• My changes generate no new compilation warnings for any of the targets.

Special treatment

• This PR needs additional PRs to work (list the PRs, preferably in merge-order).
• I will merge this PR by myself when appropriate.

[github-actions]

Unit Test Results

5 734 tests  ±0   5 095 ✔️ ±0   27m 44s ⏱️ - 1m 11s
   311 suites ±0      639 💤 ±0 
       1 files   ±0          0 ❌ ±0 

Results for commit 95e4b20. ± Comparison against base commit 367c8ee.

♻️ This comment has been updated with latest results.

[adamdebek]

fixes: phoenix-rtos/phoenix-rtos-project#891

[damianloew]

When the commit solves some issue we should add the following line in the commit description:

[nalajcie]

not doing code review, but please use locking instead of mutexing in commit message title :)

[badochov]

Does it fix zedbaord target as well?

[lukileczo]

LGTM

[adamdebek]

Does it fix zedbaord target as well?

I didn't see it fail on this target, maybe scheduling differs, but if it was failing on zedboard tihs pr should also fix it.