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 <[email protected]>
Cc: Marek Vasut <[email protected]>
Cc: Aneesh Bansal <[email protected]>
Cc: Naveen Burmi <[email protected]>
Cc: Po Liu <[email protected]>
Cc: Bin Meng <[email protected]>
Cc: Alison Wang <[email protected]>
Cc: Reinhard Arlt <[email protected]>
Cc: Shengzhou Liu <[email protected]>
Cc: York Sun <[email protected]>
Signed-off-by: Tim Harvey <[email protected]>
Tested-by: Bin Meng <[email protected]>
Tested-by: Marcel Ziswiler <[email protected]>