MAINTAINERS: minor file line update

"xen/arch/arm/include/asm/tee" is a directory and should be terminated
by a slash ("/").

Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com>
Acked-by: Julien Grall <jgrall@amazon.com>
Acked-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
Acked-by: Bertrand Marquis <bertrand.marquis@arm.com>

MAINTAINERS

@@ -518,7 +518,7 @@ TEE MEDIATORS
 M:	Volodymyr Babchuk <volodymyr_babchuk@epam.com>
 M:	Bertrand Marquis <bertrand.marquis@arm.com>
 S:	Supported
-F:	xen/arch/arm/include/asm/tee
+F:	xen/arch/arm/include/asm/tee/
 F:	xen/arch/arm/tee/
 
 TOOLSTACK