modpost: move __attribute__((format(printf, 2, 3))) to modpost.h

This attribute must be added to the function declaration in a header
for comprehensive checking of all the callsites.

Fixes: 6d9a89ea4b ("kbuild: declare the modpost error functions as printf like")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>

scripts/mod/modpost.c

@@ -60,8 +60,7 @@ static unsigned int nr_unresolved;
 
 #define MODULE_NAME_LEN (64 - sizeof(Elf_Addr))
 
-void __attribute__((format(printf, 2, 3)))
-modpost_log(enum loglevel loglevel, const char *fmt, ...)
+void modpost_log(enum loglevel loglevel, const char *fmt, ...)
 {
 	va_list arglist;