mm: Fix write-strobe handling for 64B word configurations

[davidbiancolin]

Not a common configuration. Unless you're doing FPGA stuff.

Related PRs / Issues:

Type of change:

• Bug fix
• New feature
• Other enhancement

Impact:

• RTL change
• Software change (RISC-V software)
• Build system change
• Other

Contributor Checklist:

• Did you set main as the base branch?
• Is this PR's title suitable for inclusion in the changelog and have you added a changelog:<topic> label?
• Did you state the type-of-change/impact?
• Did you delete any extraneous prints/debugging code?
• Did you mark the PR with a changelog: label?
• (If applicable) Did you add documentation for the feature?
• (If applicable) Did you add a test demonstrating the PR?

• (If applicable) Did you mark the PR as Please Backport?

[jerryz123]

@abejgonzalez Do you know why this is failing? Doesn't seem to be related to this PR.

[davidbiancolin]

I did a ff merge in testchipip so the commit pointed to here is now at the head of master

[abejgonzalez]

LGTM. CI is failing due to another issue.