The TRNSYNC feature is available (and enabled) only in transparent mode.

Since commit 7cc9bda9 ("soc: fsl: cpm1: qmc: Handle timeslot entries
at channel start() and stop()") TRNSYNC register is updated in
transparent and hdlc mode. In hdlc mode, the address of the TRNSYNC
register is used by the QMC for other internal purpose. Even if no weird
results were observed in hdlc mode, touching this register in this mode
is wrong.

Update TRNSYNC only in transparent mode.

Fixes: 7cc9bda9 ("soc: fsl: cpm1: qmc: Handle timeslot entries at channel start() and stop()")
Cc: stable@vger.kernel.org
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/20240808071132.149251-2-herve.codina@bootlin.comSigned-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>