correct obviously wrong but unused ahci reset.

Reference: /n/atom/patch/applied/ahcireset
Date: Thu May 15 16:24:03 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/k10/sdahci.c	Thu May 15 16:24:03 2014
+++ /sys/src/nix/k10/sdahci.c	Thu May 15 16:24:03 2014
@@ -571,7 +571,7 @@
 
 	h->ghc |= Hhr;
 	for(wait = 0; wait < 1000; wait += 100){
-		if(h->ghc == 0)
+		if((h->ghc & Hhr) == 0)
 			return 0;
 		delay(100);
 	}