remoteproc/davinci: Use %zx for formating size_t

da8xx_rproc_mem size is of type size_t, so use %zx to format the debug
print of it to avoid a compile warning.

Acked-by: Suman Anna <s-anna@ti.com>
Reviewed-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>