Fix a bug in the previous change to restore the fast path for syscall return.  The ast() function may cause a context switch in which case PCB_FULL_IRET would be set in the pcb.  However, the code was not rechecking the flag after ast() returned and would not properly restore the FSBASE and GSBASE MSRs.  To fix, recheck the PCB_FULL_IRET flag after ast() returns.
Fix a bug in the previous change to restore the fast path for syscall
return.  The ast() function may cause a context switch in which case
PCB_FULL_IRET would be set in the pcb.  However, the code was not
rechecking the flag after ast() returned and would not properly restore
the FSBASE and GSBASE MSRs.  To fix, recheck the PCB_FULL_IRET flag after
ast() returns.

While here, trim an instruction (and memory access) from the doreti path
and fix a typo in a comment.

MFC after:	1 week

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