e1000: releasing semaphore once no longer needed

e1000: releasing semaphore once no longer needed

Once the hwsw semaphore is acquired, it must be released when access to the
hw is completed. Without this subsequent calls to acquire will timeout
obtaining the semaphore.

Cc: Marcel Ziswiler <marcel@ziswiler.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Aneesh Bansal <aneesh.bansal@freescale.com>
Cc: Naveen Burmi <NaveenBurmi@freescale.com>
Cc: Po Liu <po.liu@freescale.com>
Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Alison Wang <alison.wang@freescale.com>
Cc: Reinhard Arlt <reinhard.arlt@esd-electronics.com>
Cc: Shengzhou Liu <Shengzhou.Liu@freescale.com>
Cc: York Sun <yorksun@freescale.com>
Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>