fix build: remove unused variable

fix: "src/gprs/gprs_gmm_attach.c:240:6: error: unused variable ‘rc’"

introduced by

"gprs_gmm: Fix missing Security Command for 3G when attaching"
Change Id  I1e12b0a32e58c6f78dba7b548f7d7016567229db

Change-Id: I4837c10fed915c558a5374d448af813219087f36
1 file changed