common: nvedit: use snprintf instead of sprintf

Use snprintf to replace sprintf.

Coverity log:
"
Unbounded source buffer (STRING_SIZE)
string_size: Passing string init_val of unknown size to sprintf.
"

Reported-by: Coverity
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Tom Rini <trini@konsulko.com>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>

common/cmd_nvedit.c

@@ -595,7 +595,7 @@ static int do_env_edit(cmd_tbl_t *cmdtp, int flag, int argc,
 	/* Set read buffer to initial value or empty sting */
 	init_val = getenv(argv[1]);
 	if (init_val)
-		sprintf(buffer, "%s", init_val);
+		snprintf(buffer, CONFIG_SYS_CBSIZE, "%s", init_val);
 	else
 		buffer[0] = '\0';