fsr: preserve xfrog_bulkstat error codes

Fix the bulkstat loop condition in fsrfs() to assign the return
value of xfrog_bulkstat() to ret before comparing it against zero.

Without the extra parentheses, operator precedence causes ret
to receive only the result of the comparison (0 or 1), which
discards the actual error code and breaks error reporting.

Signed-off-by: liuh <liuhuan01@kylinos.cn>
Cc: <linux-xfs@vger.kernel.org> # v5.3.0
Fixes: e6542132dec3cd ("libfrog: convert bulkstat.c functions to negative error codes")
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>