STM32 flash erase timeout fix

STM32 flash erase timeout fix

The current timeout for STM32 flash block erase and flash mass erase is
10 (ms), which is too tight, and fails around 50% of the time for me.
The data sheet for STM32F107VC specifies a maximum erase time of 40 ms
(for both operations).

I'd also consider it a bug that the code does not detect a timeout, but
just assumes that the operation has completed.  The attached patch does
not address this bug.

The attached patch increases the timeouts from 10 to 100 ms.  Please apply.

/Tobias