accel/amdxdna: Remove casting mailbox payload pointer

The mailbox payload pointer is void __iomem *. Casting it to u32 * is
incorrect and causes sparse warning.
  cast removes address space '__iomem' of expression

Fixes: b87f920b ("accel/amdxdna: Support hardware mailbox")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202501130921.ktqwsMLH-lkp@intel.com/


Signed-off-by: Lizhi Hou <lizhi.hou@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250113182617.1256094-1-lizhi.hou@amd.com