net: atm: Use IS_ENABLED in atm_dev_ioctl

When building with -Wsometimes-uninitialized, Clang warns:

net/atm/resources.c:256:6: warning: variable 'number' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
net/atm/resources.c:212:7: warning: variable 'iobuf_len' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]

Clang won't realize that compat is 0 when CONFIG_COMPAT is not set until
the constant folding stage, which happens after this semantic analysis.
Use IS_ENABLED instead so that the zero is present at the semantic
analysis stage, which eliminates this warning.

Link: https://github.com/ClangBuiltLinux/linux/issues/386
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/atm/resources.c

@@ -203,13 +203,9 @@ int atm_dev_ioctl(unsigned int cmd, void __user *arg, int compat)
 	int __user *sioc_len;
 	int __user *iobuf_len;
 
-#ifndef CONFIG_COMPAT
-	compat = 0; /* Just so the compiler _knows_ */
-#endif
-
 	switch (cmd) {
 	case ATM_GETNAMES:
-		if (compat) {
+		if (IS_ENABLED(CONFIG_COMPAT) && compat) {
 #ifdef CONFIG_COMPAT
 			struct compat_atm_iobuf __user *ciobuf = arg;
 			compat_uptr_t cbuf;
@@ -253,7 +249,7 @@ int atm_dev_ioctl(unsigned int cmd, void __user *arg, int compat)
 		break;
 	}
 
-	if (compat) {
+	if (IS_ENABLED(CONFIG_COMPAT) && compat) {
 #ifdef CONFIG_COMPAT
 		struct compat_atmif_sioc __user *csioc = arg;
 		compat_uptr_t carg;