Trivial typo fix in PppRouter

Trivial typo that prevents PppRouter from building with default makefiles.

Before patch:
```
me@box:~/tinyos-main/apps/PppRouter$ make epic blip
[...snippage...]
In component `PppRouterC':
PppRouterC.nc:63: component StaticIpAddressC not found
make: *** [exe0] Error 1
```
After patch:
```
me@box:~/tinyos-main/apps/PppRouter$ make epic blip
[...snippage...]
   compiled PppRouterC to build/epic/main.exe
          48464 bytes in ROM
           9516 bytes in RAM
msp430-objcopy --output-target=ihex build/epic/main.exe build/epic/main.ihex
writing TOS image
```