dahdi: Do not define dev_name if already backported.

RHEL 5.6 has backported dev_name in include/dahdi/devices.h.  We now need to
check for a back ported definition before defining our own version on pre
2.6.26 kernels.

(closes issue #18992)
Reported by: ndupeux, AlexCeli
Tested by: elguero

Signed-off-by: Tzafrir Cohen <tzafrir.cohen@xorcom.com>
Acked-by: Shaun Ruffell <sruffell@digium.com>

Origin: http://svnview.digium.com/svn/dahdi?view=rev&rev=9894

git-svn-id: http://svn.asterisk.org/svn/dahdi/linux/branches/2.4@9895 a0bf4364-ded3-4de4-8d8a-66a801d63aff

include/dahdi/kernel.h

@@ -87,7 +87,13 @@
 #endif
 
 #if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,26)
-#define dev_name(dev)		(dev)->bus_id
+#  ifdef RHEL_RELEASE_VERSION
+#    if RHEL_RELEASE_CODE < RHEL_RELEASE_VERSION(5, 6)
+#define dev_name(dev)		((dev)->bus_id)
+#    endif
+#  else
+#define dev_name(dev)		((dev)->bus_id)
+#  endif
 #define dev_set_name(dev, format, ...) \
 	snprintf((dev)->bus_id, BUS_ID_SIZE, format, ## __VA_ARGS__);
 #endif