drivers/net/ne2000_base.c: Fix GCC 4.6 build warnings

drivers/net/ne2000_base.c: Fix GCC 4.6 build warnings

Fix:
ne2000_base.c: In function 'dp83902a_send':
ne2000_base.c:282:7: warning: variable 'tmp' set but not used
[-Wunused-but-set-variable]
ne2000_base.c: In function 'dp83902a_RxEvent':
ne2000_base.c:376:5: warning: variable 'rsr' set but not used
[-Wunused-but-set-variable]
ne2000_base.c: In function 'dp83902a_TxEvent':
ne2000_base.c:513:5: warning: variable 'tsr' set but not used
[-Wunused-but-set-variable]
ne2000_base.c: In function 'dp83902a_ClearCounters':
ne2000_base.c:550:17: warning: variable 'cnt3' set but not used
[-Wunused-but-set-variable]
ne2000_base.c:550:11: warning: variable 'cnt2' set but not used
[-Wunused-but-set-variable]
ne2000_base.c:550:5: warning: variable 'cnt1' set but not used
[-Wunused-but-set-variable]

Signed-off-by: Wolfgang Denk <wd@denx.de>