libcamera: base: file_descriptor: Move inode() function to frame_buffer.cpp

The inode() function has always been a bit of an outcast in the
FileDescriptor class, as it's not related to the core feature provided
by FileDescriptor, a shared ownership wrapper around file descriptors.
As it's only used in the FrameBuffer implementation, move it to
frame_buffer.cpp as a static function.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

include/libcamera/base/file_descriptor.h

@@ -8,7 +8,6 @@
 #pragma once
 
 #include <memory>
-#include <sys/types.h>
 
 namespace libcamera {
 
@@ -28,8 +27,6 @@ public:
 	int fd() const { return fd_ ? fd_->fd() : -1; }
 	FileDescriptor dup() const;
 
-	ino_t inode() const;
-
 private:
 	class Descriptor
 	{