soc: fsl: cpm1: qmc: Add missing spinlock comment

checkpatch.pl raises the following issue
  CHECK: spinlock_t definition without comment

Add the missing comments.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/20240808071132.149251-23-herve.codina@bootlin.com


Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>