SMC91111: Clean up SMC_inx macros on xsengine and xaeniax

This patch fixes the following warnings:

Configuring for xaeniax board...
smc91111_eeprom.c: In function 'print_macaddr':
smc91111_eeprom.c:278: warning: suggest parentheses around + or - in operand of &
smc91111_eeprom.c:281: warning: suggest parentheses around + or - in operand of &
...
Configuring for xsengine board...
smc91111_eeprom.c: In function 'print_macaddr':
smc91111_eeprom.c:278: warning: suggest parentheses around + or - inside shift
smc91111_eeprom.c:281: warning: suggest parentheses around + or - inside shift

Signed-off-by: Ben Warren <biggerbadderben@gmail.com>