msan: notate more variable assignments from assembly code

[theuni]

This was missed in 31ba40494428dcbf2eb5eb6f2328eca91b0b0746 because older versions of clang did not complain about it. But clang-17, at least, does.

The array-as-a-param makes this annoying because sizeof(l) is not helpful. I'd be happy to change the size calculation if there are any better suggestions or strong preferences.