samples: drivers: can: Rename directory for consistency

This commit renames the CAN sample directory name from `CAN` to `can`
to be consistent with others.

Noting that the CAN driver test directory is named `tests/drivers/can`,
we have no excuse for naming the CAN driver sample directory
`samples/drivers/CAN`.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

CODEOWNERS

@@ -372,7 +372,7 @@
 /samples/bluetooth/                       @jhedberg @Vudentz @joerchan
 /samples/boards/intel_s1000_crb/          @sathishkuttan @dcpleung @nashif
 /samples/display/                         @vanwinkeljan
-/samples/drivers/CAN/                     @alexanderwachter
+/samples/drivers/can/                     @alexanderwachter
 /samples/drivers/display/                 @vanwinkeljan
 /samples/drivers/ht16k33/                 @henrikbrixandersen
 /samples/drivers/lora/                    @Mani-Sadhasivam