Convert fatal to error in remote_prepare

Convert fatal to error in remote_prepare

This commit converts a call to fatal in remote_prepare with a call to
error.  remote_prepare is called precisely once, from main, at a point
where jumping to toplevel will call exit (1), so error and fatal are
functionally equivalent at this point.  Note that remote_prepare calls
perror_with_name (which calls error) so callers of remote_prepare must
already handle the fact that it may exit via longjmp.

gdb/gdbserver/ChangeLog:

	* remote-utils.c (remote_prepare): Replace fatal with error.