rockchip: mkimage: remove (left-over) assignment w/o effect [coverity]

An assignment (of a value to itself) was left over (after removing and
addition from the line) from moving the common padding code into
rkcommon_vrec_header.

This change removes this to avoid a spurious warning in static code
analysis (i.e. Coverity).
Signed-off-by: NPhilipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reported-by: Coverity (CID: 161418)
Reviewed-by: NTom Rini <trini@konsulko.com>

tools/rkcommon.c

@@ -227,5 +227,4 @@ void rkcommon_vrec_header(struct image_tool_params *params,
 	/* Allocate, clear and install the header */
 	tparams->hdr = malloc(tparams->header_size);
 	memset(tparams->hdr, 0, tparams->header_size);
-	tparams->header_size = tparams->header_size;
 }