net: qrtr: fix type for size in smd

The return value for of_property_count_u32_elems can be negative in the
case of an error or the property is not found. It is incorrect to use
size_t, unsigned type, as this can cause an overflow. Switch size from
type size_t to int.

Change-Id: Ica0425abd034b82994ab32087f04d602ce3dd9e9
Signed-off-by: Tony Truong <quic_truong@quicinc.com>