MAINTAINERS: use the correct efi-stub location

Commit 4171fe2f8a47 ("EFI stub documentation updates") moved the file,
update the pattern.
Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Roy Franz <roy.franz@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

MAINTAINERS

@@ -3419,7 +3419,7 @@ M:	Matt Fleming <matt.fleming@intel.com>
 L:	linux-efi@vger.kernel.org
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/mfleming/efi.git
 S:	Maintained
-F:	Documentation/x86/efi-stub.txt
+F:	Documentation/efi-stub.txt
 F:	arch/ia64/kernel/efi.c
 F:	arch/x86/boot/compressed/eboot.[ch]
 F:	arch/x86/include/asm/efi.h