don't print native_fallocate() error if ENOSYS

don't print native_fallocate() error if ENOSYS

log_err(ENOSYS) on native_fallocate() failure which was newly added
by 2c3e17be('filesetup: add native fallocate') should be silenced
or somehow be printed only once instead of being a per file message.

This happens on a platform like FreeBSD where posix_fallocate(3)
exists, but native_fallocate() is ENOSYS.

This commit just silences it if errno is set to ENOSYS on return.
"native" is the default mode, thus not printing ENOSYS won't be any
confusing unless fallocate=native is explicitly specified, and
native_fallocate() has dprint() for ENOSYS case anyway.

--
 # uname
 FreeBSD
 # ./fio --name=xxx --ioengine=sync --rw=read --bs=4k --size=10m --nrfiles=20
 xxx: (g=0): rw=read, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=sync, iodepth=1
 fio-2.99-23-gdad0
 Starting 1 process
 xxx: Laying out IO files (20 files / total 10MiB)
 fio: native_fallocate call failed: Function not implemented
 fio: native_fallocate call failed: Function not implemented
 fio: native_fallocate call failed: Function not implemented
 fio: native_fallocate call failed: Function not implemented
 fio: native_fallocate call failed: Function not implemented
 fio: native_fallocate call failed: Function not implemented
 fio: native_fallocate call failed: Function not implemented
 fio: native_fallocate call failed: Function not implemented
 fio: native_fallocate call failed: Function not implemented
 fio: native_fallocate call failed: Function not implemented
 ...

Signed-off-by: Tomohiro Kusumi <tkusumi@tuxera.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>