s390: Replace weird use of PTR_RET.

Saves repeating "(void __force *)__uptr" but it's less clear.  Using
the output of PTR_RET() to determine the error rather than just
testing IS_ERR() is odd.

For example, I *assume* __gptr_to_uptr() never returns NULL?  Because
the __ret would be 0 for the old code.  The new version is clearer, IMHO:
it would try to get_user() on that address.

If you hate this variant, I can just s/PTR_RET/PTR_ERR_OR_ZERO/ instead.

Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>

arch/s390/kvm/gaccess.h

@@ -42,9 +42,11 @@ static inline void __user *__gptr_to_uptr(struct kvm_vcpu *vcpu,
 ({								\
 	__typeof__(gptr) __uptr = __gptr_to_uptr(vcpu, gptr, 1);\
 	int __mask = sizeof(__typeof__(*(gptr))) - 1;		\
-	int __ret = PTR_RET((void __force *)__uptr);		\
+	int __ret;						\
 								\
-	if (!__ret) {						\
+	if (IS_ERR((void __force *)__uptr)) {			\
+		__ret = PTR_ERR((void __force *)__uptr);	\
+	} else {						\
 		BUG_ON((unsigned long)__uptr & __mask);		\
 		__ret = get_user(x, __uptr);			\
 	}							\
@@ -55,9 +57,11 @@ static inline void __user *__gptr_to_uptr(struct kvm_vcpu *vcpu,
 ({								\
 	__typeof__(gptr) __uptr = __gptr_to_uptr(vcpu, gptr, 1);\
 	int __mask = sizeof(__typeof__(*(gptr))) - 1;		\
-	int __ret = PTR_RET((void __force *)__uptr);		\
+	int __ret;						\
 								\
-	if (!__ret) {						\
+	if (IS_ERR((void __force *)__uptr)) {			\
+		__ret = PTR_ERR((void __force *)__uptr);	\
+	} else {						\
 		BUG_ON((unsigned long)__uptr & __mask);		\
 		__ret = put_user(x, __uptr);			\
 	}							\