powerpc: 83xx: km83xx: Fix keymile vendor prefix

When kmeter.c was refactored into km83xx.c in 2011, the "keymile" vendor
prefix was changed to upper-case "Keymile". The devicetree at
arch/powerpc/boot/dts/kmeter1.dts never underwent the same change,
suggesting that this was simply a mistake.

Fixes: 93e2b95c81042d ("powerpc/83xx: rename and update kmeter1")
Signed-off-by: J. Neuschäfer <j.ne@posteo.net>
Reviewed-by: Heiko Schocher <hs@nabladev.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260303-keymile-v1-1-463a11e71702@posteo.net