libcamera: v4l2_videodevice: Don't use std::atomic specialization

The std::atomic_uint64_t specialization was missing from C++14, and only
added to C++17 (see LWG 2441). It was treated as a Defect Report and
backported to earlier C++ standards by gcc and clang, but is missing
from libstdc++ shipped with gcc 5 and gcc 6. Fix the compilation error
by using std::atomic<uint64_t> instead.

Fixes: 4e0d1eca10 ("libcamera: V4L2BufferCache: Improve cache eviction strategy")
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/libcamera/include/v4l2_videodevice.h

@@ -9,6 +9,7 @@
 
 #include <atomic>
 #include <memory>
+#include <stdint.h>
 #include <string>
 #include <vector>
 
@@ -142,7 +143,7 @@ private:
 		std::vector<Plane> planes_;
 	};
 
-	std::atomic_uint64_t lastUsedCounter_;
+	std::atomic<uint64_t> lastUsedCounter_;
 	std::vector<Entry> cache_;
 	/* \todo Expose the miss counter through an instrumentation API. */
 	unsigned int missCounter_;