CN05040 build fails

[Travis F. Collins]

C99 incompatible

iio-oscilloscope/plugins/cn0540.c

Line 175 in 304cc0f

 for(int i = 0; i < AVG_COUNT;i++) 

and line 203.

This causes build failures on older Linaro builds.

[Adrian Suciu]

Fixed with c5a79e5