iwlwifi: update error dump in testmode command sram_read

The error message will be show up by using IWL_ERR
insteads of IWl_DEBUG_INFO.

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>