smc911x: update SMC911X related configuration description

Since commit 736fead8fdbf8a8407048bebc373cd551d01ec98 "Convert SMC911X
Ethernet driver to CONFIG_NET_MULTI API" SMC911X configration options
are called CONFIG_SMC911X rather than CONFIG_DRIVER_SMC911X. Update
README to reflect that change.

Signed-off-by: Mike Rapoport <mike@compulab.co.il>

README

@@ -846,20 +846,20 @@ The following options need to be configured:
 			Define this to use i/o functions instead of macros
 			(some hardware wont work with macros)
 
-		CONFIG_DRIVER_SMC911X
+		CONFIG_SMC911X
 		Support for SMSC's LAN911x and LAN921x chips
 
-			CONFIG_DRIVER_SMC911X_BASE
+			CONFIG_SMC911X_BASE
 			Define this to hold the physical address
 			of the device (I/O space)
 
-			CONFIG_DRIVER_SMC911X_32_BIT
+			CONFIG_SMC911X_32_BIT
 			Define this if data bus is 32 bits
 
-			CONFIG_DRIVER_SMC911X_16_BIT
+			CONFIG_SMC911X_16_BIT
 			Define this if data bus is 16 bits. If your processor
 			automatically converts one 32 bit word to two 16 bit
-			words you may also try CONFIG_DRIVER_SMC911X_32_BIT.
+			words you may also try CONFIG_SMC911X_32_BIT.
 
 - USB Support:
 		At the moment only the UHCI host controller is