irqchip/mvebu-gicp: Use resource_size() for ioremap()

0-day reported an off by one in the ioremap() sizing:

  drivers/irqchip/irq-mvebu-gicp.c:240:45-48: WARNING:
  Suspicious code. resource_size is maybe missing with gicp -> res

Convert it to resource_size(), which does the right thing.

Fixes: 3c3d7dba ("irqchip/mvebu-gicp: Clear pending interrupts on init")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Closes: https://lore.kernel.org/oe-kbuild-all/202508062150.mtFQMTXc-lkp@intel.com/