cmd/geth: make import cmd exit with 1 if import errors occurred (#21244)

The import command should not return a 0 status
code if the import finishes prematurely becaues
of an import error.

Returning the error causes the program to exit with 1
if the err is non nil.

Signed-off-by: meows <b5c6@protonmail.com>
# Conflicts:
#	cmd/geth/chaincmd.go