scripts/nsdeps: use alternative sed delimiter

When doing an out of tree build with O=, the nsdeps script constructs
the absolute pathname of the module source file so that it can insert
MODULE_IMPORT_NS statements in the right place. However, ${srctree}
contains an unescaped path to the source tree, which, when used in a sed
substitution, makes sed complain:

++ sed 's/[^ ]* *//home/jeyu/jeyu-linux\/&/g'
sed: -e expression #1, char 12: unknown option to `s'

The sed substitution command 's' ends prematurely with the forward
slashes in the pathname, and sed errors out when it encounters the 'h',
which is an invalid sed substitution option. To avoid escaping forward
slashes ${srctree}, we can use '|' as an alternative delimiter for
sed instead to avoid this error.

Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Matthias Maennich <maennich@google.com>
Tested-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Jessica Yu <jeyu@kernel.org>