e1000: fix unused variable waring for e1000 driver

Fix the following build warning in drivers/net/e1000.c

e1000.c: In function 'e1000_reset_hw':
e1000.c:1373:11: warning: variable 'icr' set but not used [-Wunused-but-set-variable]
e1000.c: In function 'e1000_phy_init_script':
e1000.c:4395:11: warning: variable 'ret_val' set but not used [-Wunused-but-set-variable]

Signed-off-by: Roy Zang <tie-fei.zang@freescale.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Kyle Moffett <Kyle.D.Moffett@boeing.com>