Mk/Uses/cargo.mk: Fix crate name and version split (take 2)

cargo.mk is still too eager in splitting a crate's name and version
in two when the name contains a dash followed by a number. For
example with utf-8-0.7.4 the wrong URL ends up being used in
MASTER_SITES

.../utf/8-0.7.4/download/...

instead of

.../utf-8/0.7.4/download/...

PR: 230413
Reported by: Thomas Hurst <tom@hur.st>