prismtech: Avoid recompile when changing compile dir

-I$(PWD) is superflous - and caused absolute path to be stored in build command - this
casuses recompile when using symlink to kernel.
Also deleted commented out -DCONFIG_PRISM_WDS. CONFIG_PRISM_WDS are not present in
any of the source files.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

drivers/net/wireless/prism54/Makefile

@@ -6,5 +6,3 @@ prism54-objs := islpci_eth.o islpci_mgt.o \
 
 obj-$(CONFIG_PRISM54) += prism54.o
 
-EXTRA_CFLAGS = -I$(PWD) #-DCONFIG_PRISM54_WDS
-