ath10k: remove redundant -ve check against u32 integer size

Variable section_table.size is a u32 and so cannot be less than
zero, hence the less than zero check is redundant and can be
removed.

Detected by CoverityScan, CID#1463855 ("Unsigned compared against 0")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>