sgi575/run_model.sh: fix mcp uart out file

MCP firmware uses css uart in MCP address space rather than soc uart.
Fix the MCP's uart out file to use css uart.

Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Change-Id: Id9b26de7349e5303e6abb64df5ee4a4babb7d860