powerpc: fix spelling mistake: "Usupported" -> "Unsupported"

[Michael Ellerman]

On Fri, 2018-03-30 at 15:55:53 UTC, Colin King wrote:
> From: Colin Ian King <colin.king at canonical.com>
> 
> Trivial fix to spelling mistake in bootx_printf message text
> 
> Signed-off-by: Colin Ian King <colin.king at canonical.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/e6536a9f94c00a5e1da0a869ccea07

cheers