sysreset: at91: Correct Makefile rule for SYSRESET_AT91

The SPL_TPL part is in the wrong place. Fix it.

Signed-off-by: Simon Glass <sjg@chromium.org>
Fixes: 71d4393f ("sysreset: Add Atmel/Microchip sysreset driver")
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>