modprobe: don't attempt to remove an already removed module

modprobe: don't attempt to remove an already removed module

In a scenario like following:
    # lsmod | grep -e bnx2i -e cnic
    bnx2i                  94208  0
    libiscsi               94208  1 bnx2i
    cnic                   90112  1 bnx2i
    uio                    32768  1 cnic
    scsi_transport_iscsi   196608  2 bnx2i,libiscsi

    # modprobe -v --remove --remove-holders cnic
    rmmod bnx2i
    rmmod cnic
    rmmod libiscsi
    rmmod cnic
    modprobe: ERROR: libkmod/libkmod-module.c:856 kmod_module_remove_module()
    could not remove 'cnic': No such file or directory

modprobe attempts to remove cnic module twice and propagates that error
to the user with a message as well as an exit code.

Add a check to avoid attempts to remove modules that are already gone.

Signed-off-by: Jan Stancek <jstancek@redhat.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/pull/393
Signed-off-by: Lucas De Marchi <demarchi@kernel.org>