adb: Avoid a couple std::string constructions

With some internal API changing from "const char*" to
"const std::string&", we can change a couple calling sites to
directly pass a std::string reference, instead of getting the
c_str() version of the string.  This avoids us creating a
temporary std::string for the call.

Test: TreeHugger
Change-Id: I2fe0760ce8bf7d352010a341005356c0a801d351