EmbeddedPkg: CodeQL Fixes.

Makes changes to comply with alerts raised by CodeQL.

Most of the issues here fall into the following two categories:

1. Potential use of uninitialized pointer.
2. Inconsistent integer width in comparison.

Co-authored-by: Taylor Beebe <taylor.d.beebe@gmail.com>
Co-authored-by: Ken Lautner <kenlautner3@gmail.com>
Co-authored-by: Bret Barkelew <bret@corthon.com>
Signed-off-by: Vineel Kovvuri[MSFT] <vineelko@microsoft.com>

EmbeddedPkg/Library/PrePiHobLib/Hob.c

@@ -498,6 +498,9 @@ BuildGuidDataHob (
   ASSERT (Data != NULL || DataLength == 0);
 
   HobData = BuildGuidHob (Guid, DataLength);
+  if (HobData == NULL) {
+    return NULL;
+  }
 
   return CopyMem (HobData, Data, DataLength);
 }

EmbeddedPkg/Library/PrePiLib/FwVol.c

@@ -283,7 +283,7 @@ FfsProcessSection (
 {
   EFI_STATUS                Status;
   UINT32                    SectionLength;
-  UINT32                    ParsedLength;
+  UINTN                     ParsedLength;
   EFI_COMPRESSION_SECTION   *CompressionSection;
   EFI_COMPRESSION_SECTION2  *CompressionSection2;
   UINT32                    DstBufferSize;

EmbeddedPkg/SimpleTextInOutSerial/SimpleTextInOut.c

@@ -504,6 +504,9 @@ OutputString (
 
   Size         = StrLen (String) + 1;
   OutputString = AllocatePool (Size);
+  if (OutputString == NULL) {
+    return EFI_OUT_OF_RESOURCES;
+  }
 
   // If there is any non-ascii characters in String buffer then replace it with '?'
   // Eventually, UnicodeStrToAsciiStr API should be fixed.