libcamera: MappedFrameBuffer: Print errno on mmap() failure

In mmap() error handling path, errno is stored but never printed
in the error log. Print it.

Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/mapped_framebuffer.cpp

@@ -182,7 +182,8 @@ MappedFrameBuffer::MappedFrameBuffer(const FrameBuffer *buffer, MapFlags flags)
 				     MAP_SHARED, plane.fd.fd(), 0);
 		if (address == MAP_FAILED) {
 			error_ = -errno;
-			LOG(Buffer, Error) << "Failed to mmap plane";
+			LOG(Buffer, Error) << "Failed to mmap plane: "
+					   << strerror(-error_);
 			break;
 		}