emulex/benet: Annotate flash_cookie as nonstring

GCC 15's new -Wunterminated-string-initialization notices that the 32
character "flash_cookie" (which is not used as a C-String)
needs to be marked as "nonstring":

drivers/net/ethernet/emulex/benet/be_cmds.c:2618:51: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (17 chars into 16 available) [-Wunterminated-string-initialization]
 2618 | static char flash_cookie[2][16] = {"*** SE FLAS", "H DIRECTORY *** "};
      |                                                   ^~~~~~~~~~~~~~~~~~

Add this annotation, avoid using a multidimensional array, but keep the
string split (with a comment about why). Additionally mark it const
and annotate the "cookie" member that is being memcmp()ed against as
nonstring too.

Signed-off-by: Kees Cook <kees@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250416221028.work.967-kees@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/emulex/benet/be_cmds.c

@@ -2615,7 +2615,11 @@ err:
 	return status;
 }
 
-static char flash_cookie[2][16] = {"*** SE FLAS", "H DIRECTORY *** "};
+/*
+ * Since the cookie is text, add a parsing-skipped space to keep it from
+ * ever being matched on storage holding this source file.
+ */
+static const char flash_cookie[32] __nonstring = "*** SE FLAS" "H DIRECTORY *** ";
 
 static bool phy_flashing_required(struct be_adapter *adapter)
 {

drivers/net/ethernet/emulex/benet/be_cmds.h

@@ -1415,7 +1415,7 @@ struct flash_section_entry {
 } __packed;
 
 struct flash_section_info {
-	u8 cookie[32];
+	u8 cookie[32] __nonstring;
 	struct flash_section_hdr fsec_hdr;
 	struct flash_section_entry fsec_entry[32];
 } __packed;