ichsmb: fix block read operation

First of all and unlike I2C, it's not the master that dictates how many
bytes to read in block read operation. It's the device that informs the
master how many bytes it's sending back.

Thus, for ichsmb_bread() the count parameter is purely an output
parameter. The code has been changed to reflect that.
The sanity checking of the response length is now done once it (the
first byte of the response) is received.

While here, handling of ICH_HST_STA_FAILED status bit has been added.
Plus some code style improvements and some new code comments in the
vicinity of the changed code.