cxgb4: fix thermal zone build error

with CONFIG_THERMAL=m and cxgb4 as built-in build fails, and
'commit e70a57fa ("cxgb4: fix thermal configuration dependencies")'
tries to fix it but when cxgb4i is made built-in build fails again,
use IS_REACHABLE instead of IS_ENABLED to fix the issue.

Fixes: e70a57fa (cxgb4: fix thermal configuration dependencies)
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/Kconfig

@@ -67,7 +67,6 @@ config CHELSIO_T3
 config CHELSIO_T4
 	tristate "Chelsio Communications T4/T5/T6 Ethernet support"
 	depends on PCI && (IPV6 || IPV6=n)
-	depends on THERMAL || !THERMAL
 	select FW_LOADER
 	select MDIO
 	select ZLIB_DEFLATE

drivers/net/ethernet/chelsio/cxgb4/Makefile

@@ -12,6 +12,4 @@ cxgb4-objs := cxgb4_main.o l2t.o smt.o t4_hw.o sge.o clip_tbl.o cxgb4_ethtool.o
 cxgb4-$(CONFIG_CHELSIO_T4_DCB) +=  cxgb4_dcb.o
 cxgb4-$(CONFIG_CHELSIO_T4_FCOE) +=  cxgb4_fcoe.o
 cxgb4-$(CONFIG_DEBUG_FS) += cxgb4_debugfs.o
-ifdef CONFIG_THERMAL
-cxgb4-objs += cxgb4_thermal.o
-endif
+cxgb4-$(CONFIG_THERMAL) += cxgb4_thermal.o

drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c

@@ -5863,7 +5863,7 @@ static int init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
 	if (!is_t4(adapter->params.chip))
 		cxgb4_ptp_init(adapter);
 
-	if (IS_ENABLED(CONFIG_THERMAL) &&
+	if (IS_REACHABLE(CONFIG_THERMAL) &&
 	    !is_t4(adapter->params.chip) && (adapter->flags & FW_OK))
 		cxgb4_thermal_init(adapter);
 
@@ -5932,7 +5932,7 @@ static void remove_one(struct pci_dev *pdev)
 
 		if (!is_t4(adapter->params.chip))
 			cxgb4_ptp_stop(adapter);
-		if (IS_ENABLED(CONFIG_THERMAL))
+		if (IS_REACHABLE(CONFIG_THERMAL))
 			cxgb4_thermal_remove(adapter);
 
 		/* If we allocated filters, free up state associated with any