obmc-flash-bmc: Ignore SC2295

With the updated openbmc-build-scripts shellcheck reports SC2295 error.
Ignore this error to make CI pass.

Signed-off-by: Lei YU <yulei.sh@bytedance.com>
Change-Id: I7b532aa9ba477bad8169e15b51bc2d19a2a066b6
diff --git a/obmc-flash-bmc b/obmc-flash-bmc
index 54dfbc9..67e3a88 100644
--- a/obmc-flash-bmc
+++ b/obmc-flash-bmc
@@ -514,6 +514,7 @@
   # Get root device /dev/mmcblkpX
   rootmatch=" on / "
   root="$(mount | grep "${rootmatch}")"
+  # shellcheck disable=SC2295
   root="${root%${rootmatch}*}"
 
   # Find the device label