cam_dev silhs bug fix

[bstephens82]

Resolves #844.

This additional code in cam_dev/micro_pumas_cam.F90 will allow a run using cam_dev and SILHS, i.e. something like

CAM_CONFIG_OPTS="-phys cam_dev -silhs -psubcols 4"

to run without hitting the pcols*psubcols abort error in subcol.F90. This code is not super familiar to me, so my proposed fix (worked out with advice from @cacraigucar) may not be optimal yet, however I've tested it and it does work to get past the error and the model appears to be running normally afterward although I have not performed a months-long test yet.

Furthermore, this will not resolve a separate problem which seems more general to any subcolumns, where subcolumns print as zeros in the netcdf history files. See issue #1015 for more info about that.