iwlwifi: range check to testmode direct reg access

Added a check on the direct register access.
Checks that the address is in the lower ragnge (0x0-0x2000),
which belongs to CSR, HBUS and FH registers.

Signed-off-by: Amit Beka <amit.beka@intel.com>
Signed-off-by: Wey-Yi W Guy <wey-yi.w.guy@intel.com>