fix KernelLseek lock leak

Co-authored-by: Stefanos Costa <stefanos.costa1999@gmail.com>

src/kernel/fileSystem.cpp

@@ -803,7 +803,7 @@ int64_t KYTY_SYSV_ABI KernelLseek(int d, int64_t offset, int whence) {
 		return KERNEL_ERROR_ESPIPE;
 	}
 
-	file->mutex.Lock();
+	Common::LockGuard lock(file->mutex);
 
 	bool is_invalid = file->f.IsInvalid();
 
@@ -828,8 +828,6 @@ int64_t KYTY_SYSV_ABI KernelLseek(int d, int64_t offset, int whence) {
 
 	EXIT_IF(pos != offset);
 
-	file->mutex.Unlock();
-
 	if (is_invalid) {
 		LOGF("\tfile is invalid\n");
 		return KERNEL_ERROR_EIO;