update nanobench Valgrind suppression

start_keepalive is static, so it's likely inlined.
We'll put a ... where it goes to allow that.

C.f. https://uberchromegw.corp.google.com/i/client.skia/builders/Test-Ubuntu-GCC-ShuttleA-GPU-GTX550Ti-x86_64-Release-Valgrind/builds/529/steps/nanobench%20--abandonGpuContext/logs/stdio

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1562433002

TBR=egdaniel@google.com

Review URL: https://codereview.chromium.org/1562433002
1 file changed