MAINTAINERS: set maintainer for doc/api/efi.rst

doc/api/efi.rst belongs to the UEFI sub-system documentation.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/MAINTAINERS b/MAINTAINERS
index 82e4159..1842569 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -563,6 +563,7 @@
 R:	Alexander Graf <agraf@csgraf.de>
 S:	Maintained
 T:	git https://gitlab.denx.de/u-boot/custodians/u-boot-efi.git
+F:	doc/api/efi.rst
 F:	doc/uefi/*
 F:	include/capitalization.h
 F:	include/charset.h