Fix memory leakage with MBR on exiting error path

[ccli8]

Description

This PR fixes memory leakage on exiting error path in MBRBlockDevice::init.

Pull request type

[X] Fix
[ ] Refactor
[ ] New target
[ ] Feature
[ ] Breaking change

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2491
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7384/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : FAILURE

Build number : 2131
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7384/

[mbed-ci]

Test : FAILURE

Build number : 2266
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7384/2266

[0xc0170]

Ci error, restarting

/morph test
/morph export-build

[mbed-ci]

Test : FAILURE

Build number : 2267
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7384/2267

[0xc0170]

/morph build

[mbed-ci]

Exporter Build : FAILURE

Build number : 2132
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7384/

[0xc0170]

I accidentally closed this, restarting build, should also re-trigger exporters (pipe closed failure)

[mbed-ci]

Build : SUCCESS

Build number : 2495
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7384/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Build : SUCCESS

Build number : 2495
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7384/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 2136
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7384/

[mbed-ci]

Exporter Build : SUCCESS

Build number : 2139
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7384/

[mbed-ci]

Exporter Build : SUCCESS

Build number : 2139
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7384/

[mbed-ci]

Test : SUCCESS

Build number : 2271
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7384/2271