gdb: sim: check return value of sim_create_inferior

gdb: sim: check return value of sim_create_inferior

The current gdbsim_create_inferior func doesn't check the return value
of sim_create_inferior which can be problematic when that func doesn't
return success.  So, if it fails, call error() and be done.

Reported-by: Richard Stuckey <richard.stuckey@arc.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>