testsuite: Fix gcc.target/arm/mve/mve_vadcq_vsbcq_fpscr_overwrite.c

The test was declaring 'int *carry;' and wrote to '*carry' without
initializing 'carry' first, leading to an attempt to write at address
zero, and a crash.

Fix by declaring 'int carry;' and passing '&carrry' instead of 'carry'
as parameter.

2023-09-08  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/testsuite/
	* gcc.target/arm/mve/mve_vadcq_vsbcq_fpscr_overwrite.c: Fix.