nvmem: imx-ocotp: fix MAC address byte length

nvmem: imx-ocotp: fix MAC address byte length

The commit "13bcd440f2ff nvmem: core: verify cell's raw_len" caused an
extension of the "mac-address" cell from 6 to 8 bytes due to word_size
of 4 bytes. This led to a required byte swap of the full buffer length,
which caused truncation of the mac-address when read.

Previously, the mac-address was incorrectly truncated from
70:B3:D5:14:E9:0E to 00:00:70:B3:D5:14.

Fix the issue by swapping only the first 6 bytes to correctly pass the
mac-address to the upper layers.

Fixes: 13bcd440f2ff ("nvmem: core: verify cell's raw_len")
Cc: stable@vger.kernel.org
Signed-off-by: Steffen Bätz <steffen@innosonix.de>
Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Srinivas Kandagatla <srini@kernel.org>
Link: https://lore.kernel.org/r/20250712181729.6495-3-srini@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>