meta-facebook: yosemite4: refactor common function for stability

Refactor `check_nuvoton_board` function to avoid some scritps define
`set -e` in the beginning of `#!/bin/bash` that will think failed when
return value is non-zero and related services might got failed also.

Tested:
Run related services successfully.
root@bmc:/# systemctl status yosemite4-sys-init.service
bmc systemd[1]: Starting Yosemite4 Early System Init...
bmc systemd[1]: yosemite4-sys-init.service: Deactivated successfully.
bmc systemd[1]: Finished Yosemite4 Early System Init.

root@bmc:/# systemctl status mctpd.service
* mctpd.service - MCTP control protocol daemon
    Drop-In: /usr/lib/systemd/system/mctpd.service.d
             `-setup-local-eid.conf, setup-static-endpoints.conf

Signed-off-by: Tim Lee <timlee660101@gmail.com>
Change-Id: I6045d6ae6349cf84f0e920e4d219def602515809
diff --git a/meta-facebook/meta-yosemite4/recipes-yosemite4/plat-tool/files/yosemite4-common-functions b/meta-facebook/meta-yosemite4/recipes-yosemite4/plat-tool/files/yosemite4-common-functions
index 4e948e6..5c69011 100644
--- a/meta-facebook/meta-yosemite4/recipes-yosemite4/plat-tool/files/yosemite4-common-functions
+++ b/meta-facebook/meta-yosemite4/recipes-yosemite4/plat-tool/files/yosemite4-common-functions
@@ -22,9 +22,7 @@
 
 check_nuvoton_board()
 {
-    check_nuvoton=$(grep nuvoton /sys/firmware/devicetree/base/compatible)
-    if [ "$check_nuvoton" != "" ]; then
-        return 1
-    fi
+    set +e
+    grep nuvoton /sys/firmware/devicetree/base/compatible
     return 0
 }