NTB: ntb_test: Fix bug when counting remote files

When remote files are counted in get_files_count, without using SSH,
the code returns 0 because there is a colon prepended to $LOC. $VPATH
should have been used instead of $LOC.

Fixes: 06bd0407

 ("NTB: ntb_test: Update ntb_tool Scratchpad tests")
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Allen Hubbe <allenbh@gmail.com>
Tested-by: Alexander Fomichev <fomichev.ru@gmail.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>