MAINTAINERS: Update ibmveth maintainer

Add Nick Child as the maintainer of the IBM Power Virtual Ethernet
Device Driver, replacing Cristobal Forno.
Signed-off-by: Nick Child <nnac123@linux.ibm.com>
Link: https://lore.kernel.org/r/20220803155246.39582-1-nnac123@linux.ibm.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

MAINTAINERS

@@ -9609,7 +9609,7 @@ F:	arch/powerpc/platforms/powernv/copy-paste.h
 F:	arch/powerpc/platforms/powernv/vas*
 
 IBM Power Virtual Ethernet Device Driver
-M:	Cristobal Forno <cforno12@linux.ibm.com>
+M:	Nick Child <nnac123@linux.ibm.com>
 L:	netdev@vger.kernel.org
 S:	Supported
 F:	drivers/net/ethernet/ibm/ibmveth.*