libcamera: log: Add a LogInvalid entry to LogSeverity

enum LogSeverity values are assigned or compared to -1 to flag invalid
log severities. This generates compilation warnings with clang. Fix it
by adding an explicit LogInvalid entry to the enumeration.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/include/log.h

@@ -12,7 +12,8 @@
 namespace libcamera {
 
 enum LogSeverity {
-	LogDebug,
+	LogInvalid = -1,
+	LogDebug = 0,
 	LogInfo,
 	LogWarning,
 	LogError,