riscv: Handle invalid L2 entries in pmap_extract()

[markj]

Summary

While here, eliminate a single-use local variable.

PR: 266103

[mhorne]

sys/riscv/riscv/pmap.c

912

I guess the comment means we are unable to allocate 1G leaf pages?

916

I think the parens are wrong, it should be:

((l2 = pmap_load(l2p)) & PTE_V) != 0

Otherwise the value assigned to l2 might be PTE_V, I'm not sure about operator precedence here.

917

Optionally; this is the prevalent style.

[markj]

Handle Mitchell's comments.

[markj]

sys/riscv/riscv/pmap.c

912

Yes, I believe so.

[mhorne]

sys/riscv/riscv/pmap.c

917

You still have redundant parenthesis around pmap_load(l2p).