target/riscv-013: fix unused initialization

target/riscv-013: fix unused initialization

Scan-build reports:
	Unused code: Dead initialization
	riscv-013.c:2362 Value stored to 'control' during its
		initialization is never read

Remove the initialization of variable 'control'.

Change-Id: I548f8175530b9a2aa4c1788549d6467bf9824584
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/7206
Reviewed-by: Tim Newsome <tim@sifive.com>
Reviewed-by: Jan Matyas <matyas@codasip.com>
Tested-by: jenkins