mac80211: Fix clang warning about constant operand in logical operation

When clang detects a non-boolean constant in a logical operation it
generates a 'constant-logical-operand' warning. In
ieee80211_try_rate_control_ops_get() the result of strlen(<const str>)
is used in a logical operation, clang resolves the expression to an
(integer) constant at compile time when clang's builtin strlen function
is used.

Change the condition to check for strlen() > 0 to make the constant
operand boolean and thus avoid the warning.
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rate.c

@@ -174,9 +174,11 @@ ieee80211_rate_control_ops_get(const char *name)
 		/* try default if specific alg requested but not found */
 		ops = ieee80211_try_rate_control_ops_get(ieee80211_default_rc_algo);
 
-	/* try built-in one if specific alg requested but not found */
-	if (!ops && strlen(CONFIG_MAC80211_RC_DEFAULT))
+	/* Note: check for > 0 is intentional to avoid clang warning */
+	if (!ops && (strlen(CONFIG_MAC80211_RC_DEFAULT) > 0))
+		/* try built-in one if specific alg requested but not found */
 		ops = ieee80211_try_rate_control_ops_get(CONFIG_MAC80211_RC_DEFAULT);
+
 	kernel_param_unlock(THIS_MODULE);
 
 	return ops;