libcamera: Fix spellings and grammar

Fix a number of spelling errors and word duplications throughout the comments
within libcamera.

These were picked up with spellintian.

Also one capitalisation of the first word of a \return statement picked
up by checkstyle.py while creating this patch.

Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/buffer.cpp

@@ -321,7 +321,7 @@ Buffer::Buffer(unsigned int index, const Buffer *metadata)
  * \fn Buffer::timestamp()
  * \brief Retrieve the time when the buffer was processed
  *
- * The timestamp is expressed as a number number of nanoseconds since the epoch.
+ * The timestamp is expressed as a number of nanoseconds since the epoch.
  *
  * \return Timestamp when the buffer was processed
  */