Use vma_lookup() to walk the tree to the start value requested.  If the
vma at the start does not match, then the answer is NULL and there is no
need to look at the next vma the way that find_vma() would.

Link: https://lkml.kernel.org/r/20220906194824.2110408-21-Liam.Howlett@oracle.comSigned-off-by: NLiam R. Howlett <Liam.Howlett@Oracle.com>
Reviewed-by: NVlastimil Babka <vbabka@suse.cz>
Tested-by: NYu Zhao <yuzhao@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>