meta-z: layer.conf: set BBFILE_PATTERN

Bitbake uses this regex to associate recipes and bbappends from BBFILES
(which contains recipes and bbappends from -all- layers listed in
bblayers.conf) to this layer.  The association is then used to map the
BBFILE_PRIORITY value for this layer onto the recipes provided by this
layer.

BBFILE_PRIORITY is used to determine which recipe to use when the same
recipe appears in multiple layers.

Without BBFILE_PATTERN set, recipes in this layer will get a default
priority and not the priority specified in BBFILE_PRIORITY.

This layer doesn't set a priority anyway, so functionally this patch is
a noop but it is an improvement from a correctness standpoint, and it
makes a warning go away:

WARNING: No bb files matched BBFILE_PATTERN_foo-layer

Change-Id: Ibbbe41da6163b8e0e22b638996d01553ea51eec4
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-z/conf/layer.conf b/meta-z/conf/layer.conf
index 252db1d..7b54230 100644
--- a/meta-z/conf/layer.conf
+++ b/meta-z/conf/layer.conf
@@ -2,4 +2,4 @@
 BBPATH .= ":${LAYERDIR}"
 
 BBFILE_COLLECTIONS += "ibm-z-layer"
-BBFILE_PATTERN_ibm-z-layer = ""
+BBFILE_PATTERN_ibm-z-layer := "^${LAYERDIR}/"