soc/amd/stoneyridge: Fix get_cpu_count()

In commit 41baf0c3ff (soc/amd/stoneyridge: Remove dev_find_slot where
possible), the register being read was changed accidentally from
HT_DEV (Device 18h, Func 0) to NB_DEV (Device 18h, Func 5)

This doesn't return the correct value, and causes Grunt to reboot.

BUG=b:118721473
TEST=Boot grunt

Change-Id: I7b73358a074dd27639aafead7c8b39f0fad5685f
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/29367
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Daniel Kurtz <djkurtz@google.com>
Reviewed-by: Richard Spiegel <richard.spiegel@silverbackltd.com>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

src/soc/amd/stoneyridge/cpu.c

@@ -55,7 +55,7 @@ static void pre_mp_init(void)
 
 static int get_cpu_count(void)
 {
-	return (pci_read_config16(SOC_NB_DEV, D18F0_CPU_CNT) & CPU_CNT_MASK)
+	return (pci_read_config16(SOC_HT_DEV, D18F0_CPU_CNT) & CPU_CNT_MASK)
 									+ 1;
 }