fw_cfg: replace ioport data read with generic method

fw_cfg: replace ioport data read with generic method

IOPort read access is limited to one byte at a time by
fw_cfg_comb_valid(). As such, fw_cfg_comb_read() may safely
ignore its size argument (which will always be 1), and simply
call its fw_cfg_read() helper function once, returning 8 bits
via the least significant byte of a 64-bit return value.

This patch replaces fw_cfg_comb_read() with the generic method
fw_cfg_data_read(), and removes the unused fw_cfg_read() helper.

When called with size = 1, fw_cfg_data_read() acts exactly like
fw_cfg_read(), performing the same set of sanity checks, and
executing the while loop at most once (subject to the current
read offset being within range).

Cc: Laszlo Ersek <[email protected]>
Cc: Gerd Hoffmann <[email protected]>
Cc: Marc Marí <[email protected]>
Signed-off-by: Gabriel Somlo <[email protected]>
Message-id: 1446733972[email protected]
Reviewed-by: Laszlo Ersek <[email protected]>
Signed-off-by: Gerd Hoffmann <[email protected]>