fix(st): make metadata_block_spec static

This issue was triggered by sparse tool:
plat/st/common/stm32mp_fconf_io.c:31:17: warning:
 symbol 'metadata_block_spec' was not declared. Should it be static?

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I283d15792ed0e7ac5181e18aaf54010a0e61b370
diff --git a/plat/st/common/stm32mp_fconf_io.c b/plat/st/common/stm32mp_fconf_io.c
index 0b6cc78..1a59f0b 100644
--- a/plat/st/common/stm32mp_fconf_io.c
+++ b/plat/st/common/stm32mp_fconf_io.c
@@ -28,7 +28,7 @@
 #endif
 
 #if (STM32MP_SDMMC || STM32MP_EMMC) && PSA_FWU_SUPPORT
-io_block_spec_t metadata_block_spec = {
+static io_block_spec_t metadata_block_spec = {
 	.offset = 0,    /* To be filled at runtime */
 	.length = 0,    /* To be filled at runtime */
 };