.checkpatch.conf: ignore udelay->usleep_range warnings

usleep_range() is a Linux facility, ignore it when udelay()
is encountered.

Signed-off-by: Matt Porter <mporter@ti.com>

.checkpatch.conf

@@ -15,3 +15,6 @@
 
 # enable more tests
 --strict
+
+# Not Linux, so we don't recommend usleep_range() over udelay()
+--ignore USLEEP_RANGE