misc: Fix warnings on Cerbero's mingw (gcc 4.7)

error: this decimal constant is unsigned only in ISO C90 [-Werror]
8 jobs from fix-mingw-warnings in 14 minutes and 51 seconds (queued for 3 minutes and 6 seconds)
Status Job ID Name Coverage
  Preparation
passed #100647
gst indent

00:00:36

passed #100646
manifest

00:00:37

 
  Build
passed #100648
build fedora x86_64

00:02:08

 
  Test
passed #100649
check fedora

00:03:30

 
  Full Builds
passed #100650
build android arm64 api28

00:03:07

passed #100652
build cerbero cross win32

00:06:26

passed #100653
build cerbero cross win64

00:08:12

passed #100651
build cerbero fedora x86_64

00:07:14