factory_install: Don't print stderr from tpmc read error

tpmc read error happens when FWMP is not set. Remove stderr logs so it's
not viewed as a bug.

BUG=None
TEST=manual test on DUT

Change-Id: Ic6c50d1f37ebbb80b8d4f92424bbf52bd08cf0e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/factory_installer/+/3131253
Tested-by: Cheng-Han Yang <chenghan@chromium.org>
Reviewed-by: Yun-Kai Lin <kevinptt@chromium.org>
Commit-Queue: Cheng-Han Yang <chenghan@chromium.org>
(cherry picked from commit a269f943c31f07c0ec2fadc75a1c1f0fbc39222c)
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/factory_installer/+/3131259
diff --git a/factory_install.sh b/factory_install.sh
index 45fc372..0884221 100644
--- a/factory_install.sh
+++ b/factory_install.sh
@@ -225,7 +225,7 @@
   fi
 
   stop trunksd >/dev/null
-  if tpmc read 0x100a 1 >/dev/null; then
+  if tpmc read 0x100a 1 >/dev/null 2>&1; then
     # We only need the last byte of FWMP flags.
     flags="0x$(tpmc read 0x100a 5 | cut -d ' ' -f5)"
   fi