arc: core: Fix possible overrun

dyn_reg_info has MPU_DYNAMIC_REGION_AREAS_NUM elements, just changing
the if check to be greater equal to this number to avoid access
MPU_DYNAMIC_REGION_AREAS_NUM element causing an out-of-bounds write.

CID: 205648
Fixes #20487

Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>