[PATCH] doc: fix build with sphinx 5.0 and later.

[Heinrich Schuchardt]

On 11/7/22 14:49, Quentin Schulz wrote:
> From: Quentin Schulz <quentin.schulz at theobroma-systems.com>
>
> Sphinx 5.0 and later fails to build when language is set to None:
> Warning, treated as error:
> Invalid configuration value found: 'language = None'. Update your configuration to a valid langauge code. Falling back to 'en' (English)
>
> Let's set the language to English since it is the language used for the
> documentation.
>
> Cc: Quentin Schulz <foss+uboot at 0leil.net>
> Signed-off-by: Quentin Schulz <quentin.schulz at theobroma-systems.com>
> ---
> Cc: u-boot at lists.denx.de

Reviewed: Heinrich Schuchardt <xypron.glpk at gmx.de>