Fix a long standing logic bug introduced in r167814.  The code was added to get RSDP from loader(8) hint via kenv(2) but the bug nullified the new code and we always fell back to the previous method, i. e., sysctlbyname(3).
Fix a long standing logic bug introduced in r167814.  The code was added to
get RSDP from loader(8) hint via kenv(2) but the bug nullified the new code
and we always fell back to the previous method, i. e., sysctlbyname(3).

MFC after:	3 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase