linux-phytec-ti

smsc95xx: check return code from control messages

This patch adds additional checks of the values returned by
smsc95xx_(read|write)_reg, and wraps their common patterns
in macros.

Signed-off-by: Steve Glendinning <steve.glendinning@shawell.net>
Signed-off-by: David S. Miller <davem@davemloft.net>