clover: Add constructor for sampler_argument.

Fix defects reported by Coverity Scan.

member_not_init_in_gen_ctor: The compiler-generated constructor for this class does not initialize s.
member_not_init_in_gen_ctor: The compiler-generated constructor for this class does not initialize st.

Signed-off-by: Vinson Lee <vlee@freedesktop.org>
35 jobs for !8657 with fix-cid-1213937 in 16 seconds (queued for 4 seconds)
detached
Status Job ID Name Coverage
  Sanity
passed #7306163
sanity

00:00:16

 
  Container
manual #7306168
aarch64 manual
arm_build
manual #7306169
manual
arm_test-base
manual #7306171
windows shell 1809 mesa manual
windows_build_vs2019
manual #7306165
manual
x86_build-base
manual #7306166
manual
x86_test-base
 
  Container 2
created #7306186
android_build
created #7306192
arm64_test
created #7306194
armhf_test
created #7306181
i386_build
created #7306174
kernel+rootfs_amd64
created #7306175
aarch64
kernel+rootfs_arm64
created #7306178
aarch64
kernel+rootfs_armhf
created #7306183
ppc64el_build
created #7306185
s390x_build
created #7306179
x86_build
created #7306188
x86_test-gl
created #7306190
x86_test-vk
 
  Meson X86 64
created #7306204
meson-clang
created #7306206
meson-clover
created #7306199
meson-clover-testing
created #7306200
gstreamer
meson-gallium
created #7306202
meson-release
created #7306195
meson-testing
created #7306197
meson-testing-asan
created #7306207
meson-vulkan
 
  Build Misc
created #7306209
meson-android
created #7306212
aarch64
meson-arm64
created #7306214
aarch64
meson-arm64-build-test
created #7306210
aarch64
meson-armhf
created #7306216
meson-i386
created #7306221
meson-mingw32-x86_64
created #7306220
kvm
meson-ppc64el
created #7306218
kvm
meson-s390x
 
  Software Renderer
created #7306223
llvmpipe-piglit-cl