Fix code order in tree-sra.c:create_access

Fix code order in tree-sra.c:create_access

If get_ref_base_and_extent returns poly_int offsets or sizes,
tree-sra.c:create_access prevents SRA from being applied to the base.
However, we haven't verified by that point that we have a valid base
to disqualify.

This originally led to an ICE on the attached testcase, but it
no longer triggers there after the introduction of IPA SRA.

2019-11-08  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-sra.c (create_access): Delay disqualifying the base
	for poly_int values until we know we have a base.

gcc/testsuite/
	* gcc.target/aarch64/sve/acle/general/inline_2.c: New test.

From-SVN: r277965