fix build error if using gbs import from .src.rpm way

fix build error if using gbs import from .src.rpm way

reproduce step:
  wget http://download.tizen.org/snapshots/TIZEN/Tizen/Tizen-Unified/tizen-unified_20231011.105835/repos/standard/source/zint-2.6.7-2.src.rpm
  gbs import zint-2.6.7-2.src.rpm
  cd zint
  gbs build -A armv7l --include-all
it will show build error like this:
  ${Patch0}: No such file or directory.

Normally, for files in packaging directory, it should use "Source" filed in spec file.
Because in gbs build logic, it will remove "patch*:" line before generating patches according to commit ids.

Change-Id: I0a17e9f782aa7791cd7dd406fe32aff5f39f3c92
Signed-off-by: wang biao <biao716.wang@samsung.com>