Log FS: clear the watchdog while erasing flash

This operation takes too long on FlyingF3 and triggers a watchdog
reset.  This prevents that, although given that the watchdog
exists for a reason, perhaps this isn't the best fix.

Fixes #446
Flash Internal: Clear watchdog when erasing sector

Because erasing the internal flash blocks code execution this
can trigger a watchdog timeout.  In this circumstance we reset
the watchdog regardless of other modules.
Flash Internal: stop watchdown firing on erase for f4

Like the F3 erasing will stop code execution and trigger a watchdog
failure.  Now we reset for each sector erased.
Merge pull request #447 from peabody124/flashfs_reset_fix

Log FS: clear the watchdog while erasing flash