ethernet: rvu-af: Remove slash from the driver name

Having a slash in the driver name leads to EIO being returned while
reading /sys/module/rvu_af/drivers content.

Remove DRV_STRING as it's not used anywhere.

Fixes: 91c6945e ("octeontx2-af: cn10k: Add RPM MAC support")
Signed-off-by: Petr Malat <oss@malat.biz>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250918152106.1798299-1-oss@malat.biz


Signed-off-by: Jakub Kicinski <kuba@kernel.org>