servo_micro: Increase maximum I2C-over-USB write and read sizes.
servo_micro: Increase maximum I2C-over-USB write and read sizes.

BRANCH=none
BUG=b:79684405
TEST=This makes block_write_size up to 254B in iteflash work,
and makes 256B verification reads work.

Change-Id: I887f0eaacc87428a4646007520f27bdf5aaa231a
Signed-off-by: Matthew Blecker <d18f4466f2802f9c78c5c14a42b8c21fdbfabfcd@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1351517
Reviewed-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec