mailbox: zynqmp-ipi: fix an Excess struct member kernel-doc warning

kernel test robot reports 2 Excess struct member warnings:

zynqmp-ipi-mailbox.c:92: warning: Excess struct member 'irq' description in 'zynqmp_ipi_mbox'
zynqmp-ipi-mailbox.c:112: warning: Excess struct member 'ipi_mboxes' description in 'zynqmp_ipi_pdata'

The second one is a false positive that is caused by the
__counted_by() attribute. Kees has posted a patch for that, so just
fix the first one.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202312150705.glrQ4ypv-lkp@intel.com/


Cc: linux-arm-kernel@lists.infradead.org
Reviewed-by: Michal Simek <michal.simek@amd.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>