Fix performance regression on lmbench select benchmark

Christian Borntraeger reported that reinstating cond_resched() with
CONFIG_PREEMPT caused a performance regression on lmbench:

For example select file 500:
23 microseconds
32 microseconds

and that's really because we totally unnecessarily do the cond_resched()
in the innermost loop of select(), which is just silly.

This moves it out from the innermost loop (which only ever loops ove the
bits in a single "unsigned long" anyway), which makes the performance
regression go away.

Reported-and-tested-by: Christian Borntraeger <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/select.c

···
 						retval++;
 					}
 				}
-				cond_resched();
 			}
 			if (res_in)
 				*rinp = res_in;
···
 				*routp = res_out;
 			if (res_ex)
 				*rexp = res_ex;
+			cond_resched();
 		}
 		wait = NULL;
 		if (retval || !*timeout || signal_pending(current))