MAINTAINERS: Fix outdated reference to modules/Kconfig.mcuboot_bootutil

The commit 837245fcecf1883d37540db04b562003918d0cf2 relocated
`modules/Kconfig.mcuboot_bootutil` to `modules/Kconfig.mcuboot`.

Signed-off-by: Stephanos Ioannidis <stephanos.ioannidis@nordicsemi.no>
diff --git a/MAINTAINERS.yml b/MAINTAINERS.yml
index ea85659..0ac6eb2 100644
--- a/MAINTAINERS.yml
+++ b/MAINTAINERS.yml
@@ -3034,7 +3034,7 @@
     - de-nordic
     - nordicjm
   files:
-    - modules/Kconfig.mcuboot_bootutil
+    - modules/Kconfig.mcuboot
     - tests/boot/test_mcuboot/
   labels:
     - manifest-mcuboot