ixgbe: Fix FW init/release, make this code a function

A gap was left in the FW release/grab code in up/down path. Fix
it by making the release/grab code a function and calling it in
appropriate locations.

Signed-off-by: Ayyappan Veeraiyan <ayyappan.veeraiyan@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>