Align MBRBlockDevice writes to underlying BlockDevice write size

[juhoeskeli]

Description

When writing MBR the write buffer was allocated such that it would not align with BlockDevice write size resulting in failure of the write operation.

It would happen here:
err = bd->program(buffer, 512-buffer_size, buffer_size);

Now the buffer_size is calculated so that the writes will be properly aligned.

Tested with STM32L486 using internal flash as storage. Without fix it is not possible to initialise partition in the internal flash.

Pull request type

[X] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Breaking change

[JanneKiiskila]

To next patch release, please.

[geky]

This looks perfect to me 👍
Thanks for this

[cmonr]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 3184
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/8262/

Triggering tests

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

[mbed-ci]

Exporter Build : SUCCESS

Build number : 2779
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/8262/

[mbed-ci]

Test : FAILURE

Build number : 2985
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/8262/2985

[cmonr]

/morph test

[mbed-ci]

Test : FAILURE

Build number : 2986
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/8262/2986

[cmonr]

sigh

/morph test

[mbed-ci]

Test : SUCCESS

Build number : 2987
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/8262/2987

[NirSonnenschein]

LGTM