submodule: fix confusing variable name

submodule: fix confusing variable name

cmd_summary reads the output of git diff, but reads in the submodule path into a
variable called name.  Since this variable does not contain the name of the
submodule, but the path, rename it to be clearer what data it actually holds.

Signed-off-by: Brian M. Carlson <redacted>
Acked-by: Jens Lehmann <redacted>
Signed-off-by: Junio C Hamano <redacted>