MAINTAINERS: correct entry for lib/efi*/

lib/efi* indicates files efi* in directory lib.
lib/efi*/ indicates all files in directories lib/efi*.

Fixes: 623b3a57 efi_selftest: provide an EFI selftest application
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>