accel/amdxdna: Fix incorrect PSP firmware size

The incorrect PSP firmware size is used for initializing. It may
cause error for newer version firmware.

Fixes: 8c9ff1b1 ("accel/amdxdna: Add a new driver for AMD AI Engine")
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Lizhi Hou <lizhi.hou@amd.com>
Link: https://lore.kernel.org/r/20250604143217.1386272-1-lizhi.hou@amd.com