PCHG: Fix potential error=maybe-uninitialized in cmd_pchg_update_write
PCHG: Fix potential error=maybe-uninitialized in cmd_pchg_update_write

block_size is necessarily initialized if cmd_pchg_update_open returns
0. Thus, it shouldn't cause error=maybe-uninitialized. This patch
explicitly initializes it to 0 in case a (incapable) compiler
complains about it.

BUG=b:182600604, b:173235954
BRANCH=none
TEST=make utils-host

Change-Id: Ifff972c32007a573ac7cf759387edeb382dccaa4
Signed-off-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2966802
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

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