MAINTAINERS: add patterns to DELL WMI EXTRAS

Signed-off-by: NJoe Perches <joe@perches.com>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

MAINTAINERS

@@ -1892,6 +1892,7 @@ F:	drivers/firmware/dcdbas.*
 DELL WMI EXTRAS DRIVER
 M:	Matthew Garrett <mjg59@srcf.ucam.org>
 S:	Maintained
+F:	drivers/platform/x86/dell-wmi.c
 
 DEVICE NUMBER REGISTRY
 M:	Torben Mathiasen <device@lanana.org>