wifi: ath12k: ahb: Replace del_timer_sync() with timer_delete_sync()

A linux-next build error was reported in [1].

This is the result of a treewide timer cleanup [2].

The ath12k AHB support has not yet landed in the tree where the
cleanup occurred, and hence a new call to del_timer_sync() was not
addressed by the treewide cleanup.

So fix that one instance.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://msgid.link/20250408105146.459dfcf5@canb.auug.org.au # [1]
Link: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=8fa7292fee5c5240402371ea89ab285ec856c916 # [2]
Link: https://patch.msgid.link/20250408-timer_delete_sync-v1-1-4dcb22f71083@oss.qualcomm.com


Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>