aarch64: Fix narrowing warning in aarch64_detect_vector_stmt_subtype

aarch64: Fix narrowing warning in aarch64_detect_vector_stmt_subtype

There is a narrowing warning in aarch64_detect_vector_stmt_subtype
about gather_load_x32_cost and gather_load_x64_cost converting from int to unsigned.
These fields are always unsigned and even the constructor for sve_vec_cost takes
an unsigned. So let's just move the fields over to unsigned.

Build and tested for aarch64-linux-gnu.

gcc/ChangeLog:

	* config/aarch64/aarch64-protos.h (struct sve_vec_cost): Change gather_load_x32_cost
	and gather_load_x64_cost fields to unsigned.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>