fw_update: Pass bytes into `wr_command` function
fw_update: Pass bytes into `wr_command` function

In `wr_command` function, we use `bytearray` to wrap the bytes argument.
However, if we pass a `str` type to `bytearray` constructor, we need to
specify the encoding.

In this case, we need to use `bytes` here.

BUG=b:172978731
BRANCH=master
TEST=1. cros_workon --host start hdctools ec-devutils
     2. sudo emerge hdctools ec-devutils
     3. The fix applies into chroot
TEST=ODM verifies in their side

Signed-off-by: kerker <kerker@chromium.org>

Change-Id: I57609c36e639cd6bd116b6f2f3a1baff02312070
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2543567
Tested-by: Henry Sun <26cd8a0b26a8449e909dff5211a18ba277320ec2@google.com>
Reviewed-by: Jack Rosenthal <d3f605bef1867f59845d4ce6e4f83b8dc9e4e0ae@chromium.org>
Commit-Queue: Henry Sun <26cd8a0b26a8449e909dff5211a18ba277320ec2@google.com>

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