Mark functions as static

Mark functions used only in the same translation unit as static. This
only includes functions that do not have a prototype in a header file
either.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Closes #10470

cmd/zfs/zfs_main.c

@@ -443,7 +443,7 @@ safe_malloc(size_t size)
 	return (data);
 }
 
-void *
+static void *
 safe_realloc(void *data, size_t size)
 {
 	void *newp;