e1000: fix mismerge skb_put.

Seems there was a bit of a fix needed to due a bad merge in the legacy
receive path.  Fixes a panic due to skb_over_panic.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>