MAINTAINERS: Fix typo in openpic_kvm.c entry

It's a .c file, not a header!

Fixes: ff8cdbb ("MAINTAINERS: Add information for OpenPIC")
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

MAINTAINERS

@@ -1399,7 +1399,7 @@ F: hw/pci-host/ppce500.c
 F: include/hw/ppc/ppc_e500.h
 F: include/hw/pci-host/ppce500.h
 F: pc-bios/u-boot.e500
-F: hw/intc/openpic_kvm.h
+F: hw/intc/openpic_kvm.c
 F: include/hw/ppc/openpic_kvm.h
 F: docs/system/ppc/ppce500.rst