cxgb4: use pgprot_writecombine() on powerpc

Commit fe3cc0d9 ("powerpc: Add
pgprot_writecombine") in benh's tree exposes the pgprot_writecombine()
API to drivers on powerpc. cxgb4 has an open-coded version of the same,
so use the common API now that it's available.
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Cc: Steve Wise <swise@opengridcomputing.com>
Cc: Anton Blanchard <anton@samba.org>
Acked-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

drivers/infiniband/hw/cxgb4/t4.h

@@ -269,11 +269,8 @@ struct t4_swsqe {
 
 static inline pgprot_t t4_pgprot_wc(pgprot_t prot)
 {
-#if defined(__i386__) || defined(__x86_64__)
+#if defined(__i386__) || defined(__x86_64__) || defined(CONFIG_PPC64)
 	return pgprot_writecombine(prot);
-#elif defined(CONFIG_PPC64)
-	return __pgprot((pgprot_val(prot) | _PAGE_NO_CACHE) &
-			~(pgprot_t)_PAGE_GUARDED);
 #else
 	return pgprot_noncached(prot);
 #endif