[wip/mavlink] Fix two issues in depend.mk

- The version stored in .pc file on current is 1.0.9, while it was
  1.0.11 at some point. Downgrade the requirement so.
- Fix a missing \ in system_search pattern

mavlink/depend.mk

@@ -14,11 +14,11 @@ PREFER.mavlink?=	robotpkg
 
 DEPEND_USE+=		mavlink
 
-DEPEND_ABI.mavlink?=	mavlink>=1.0.11
+DEPEND_ABI.mavlink?=	mavlink>=1.0.9
 DEPEND_DIR.mavlink?=	../../wip/mavlink
 
 SYSTEM_SEARCH.mavlink=\
-	include/mavlink/config.h
+	include/mavlink/config.h\
 	'lib/pkgconfig/mavlink.pc:/Version/s/[^0-9.]//gp'
 endif