qcom: rpm-smd: Fix the storage variable data type

The data that returned from smd API smd_cur_packet_size() is of the type
int. The returned value is stored in a variable pkt_sz. Declare the
variable to be of type int.

Change-Id: I1aecd007f97ed151af1b9bb9ef246e9786b3fb31
Signed-off-by: Karthik Parsha <kparsha@codeaurora.org>