ShellPkg: UefiShellDebug1CommandsLib: fix SETVAR option summary

ShellPkg: UefiShellDebug1CommandsLib: fix SETVAR option summary

The command line summary for the SETVAR command currently names "-rs"
instead of "-rt":

  SETVAR variable-name [-guid guid][-bs][-rs][-nv] [=data]

Fix it.

Cc: Jaben Carsey <jaben.carsey@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17127 6f19259b-4bc3-4df7-8a09-765794883524