build: ensure that dash isn't prepended twice to abi version suffix

build: ensure that dash isn't prepended twice to abi version suffix

The ABIV_$(pkgname) variable already is formatted so return it as-is from
the GetABISuffix macro and only filter through FormatABISuffix if we read
the raw ABI version value from a version stamp file.

This ensures that binary intra-package dependencies on ABI versioned
libraries are properly formatted.

Ref: https://github.com/openwrt/packages/issues/15871
Fixes: f6a03bff5b ("build: prepend ABI suffixes with a dash if package name ends with digit")
Signed-off-by: Jo-Philipp Wich <jo@mein.io>