smmstore: update smm store filename to use an underscore

Rename "smm store" to "smm_store".

Depends on CL:1351178.

BUG=b:120060878
TEST=None

Change-Id: Ibb225e6cf6050a538da2ddc7eedbe179d97df159
Reviewed-on: https://chromium-review.googlesource.com/c/1351857
Commit-Queue: Joel Kitching <kitching@chromium.org>
Tested-by: Joel Kitching <kitching@chromium.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
1 file changed