refactor(st): rename plat_set_image_source

The function is only used in this file and is static, no need to have
plat_ prefix. And as it is used only in case of FWU, when looking in
metadata, add it in the function name.

Suggested-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I925c9c517216cf93bd74308c280c0f22c7734490
diff --git a/plat/st/common/bl2_io_storage.c b/plat/st/common/bl2_io_storage.c
index 94017d7..c17ac7e 100644
--- a/plat/st/common/bl2_io_storage.c
+++ b/plat/st/common/bl2_io_storage.c
@@ -788,9 +788,9 @@
 	}
 }
 
-static int plat_set_image_source(unsigned int image_id,
-				 uintptr_t *handle,
-				 uintptr_t *image_spec)
+static int set_metadata_image_source(unsigned int image_id,
+				     uintptr_t *handle,
+				     uintptr_t *image_spec)
 {
 	struct plat_io_policy *policy;
 	io_block_spec_t *spec __maybe_unused;
@@ -864,6 +864,6 @@
 	assert((image_id == FWU_METADATA_IMAGE_ID) ||
 	       (image_id == BKUP_FWU_METADATA_IMAGE_ID));
 
-	return plat_set_image_source(image_id, handle, image_spec);
+	return set_metadata_image_source(image_id, handle, image_spec);
 }
 #endif /* PSA_FWU_SUPPORT */