[source] firmware-utils: fix dgn3500sum compiler warnings

[LEDE Commits]

mkresin pushed a commit to source.git, branch master:
https://git.lede-project.org/06741411e020bb28160ddd42149d6a489800dbc7

commit 06741411e020bb28160ddd42149d6a489800dbc7
Author: Mathias Kresin <dev at kresin.me>
AuthorDate: Mon Jun 26 19:22:52 2017 +0200

    firmware-utils: fix dgn3500sum compiler warnings
    
    The sum variable need to be initialised, otherwise it will points to
    random stack memory and a bogus image checksum might be calculated.
    
    While at it, fix the segfault in case the product region code isn't
    specified and enable compiler warnings which had revealed all the code
    issues.
    
    Signed-off-by: Mathias Kresin <dev at kresin.me>
---
 tools/firmware-utils/Makefile         | 2 +-
 tools/firmware-utils/src/dgn3500sum.c | 5 ++---
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/tools/firmware-utils/Makefile b/tools/firmware-utils/Makefile
index 2504678..883a7ad 100644
--- a/tools/firmware-utils/Makefile
+++ b/tools/firmware-utils/Makefile
@@ -73,7 +73,7 @@ define Host/Compile
 	$(call cc,mkdcs932, -Wall)
 	$(call cc,mkheader_gemtek,-lz)
 	$(call cc,mkrtn56uimg, -lz)
-	$(call cc,dgn3500sum)
+	$(call cc,dgn3500sum, -Wall)
 	$(call cc,edimax_fw_header, -Wall)
 	$(call cc,mkmerakifw sha1, -Wall)
 	$(call cc,mkmerakifw-old, -Wall)
diff --git a/tools/firmware-utils/src/dgn3500sum.c b/tools/firmware-utils/src/dgn3500sum.c
index 00a0c5f..eb80e6c 100644
--- a/tools/firmware-utils/src/dgn3500sum.c
+++ b/tools/firmware-utils/src/dgn3500sum.c
@@ -103,7 +103,7 @@ int main(int argc, char** argv)
   unsigned long start, i;
   char *endptr, *buffer, *p;
   int count;  // size of file in bytes
-  unsigned short sum, sum1;
+  unsigned short sum = 0, sum1 = 0;
   char sumbuf[9];
 
   if(argc < 3) {
@@ -117,7 +117,7 @@ int main(int argc, char** argv)
     printf("ERROR: File not writeable!\n");
     return 1;
   }
-  if(argc = 4)
+  if(argc == 4)
   {
     printf("%s: PID type: %s\n", argv[0], argv[3]);
     if(strcmp(argv[3], "DE")==0)
@@ -147,7 +147,6 @@ int main(int argc, char** argv)
 
   start = strtol(argv[2], &endptr, 16);
   p = buffer+start;
-  sum1 = 0;
   for(i = 0; i < count - start; i++)
   {
 	sum1 += p[i];