iwlwifi: add range checking in tm sram read command

The size of sram may alter according to ucode type.
Retrieve the maximum sram size by current ucode
type for range checking to prevent wrong data access.

Signed-off-by: Kenny Hsu <kenny.hsu@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>