ath6kl: fix size_t printf warnings

My new tracing code for ath6kl introduced these warnings on 64-bit:

trace.h:38:1: warning: format '%d' expects argument of type 'int',
	but argument 4 has type 'size_t' [-Wformat]
trace.h:61:1: warning: format '%d' expects argument of type 'int',
	but argument 4 has type 'size_t' [-Wformat]
trace.h:84:1: warning: format '%d' expects argument of type 'int',
	but argument 6 has type 'size_t' [-Wformat]
trace.h:119:1: warning: format '%d' expects argument of type 'int',
	but argument 7 has type 'size_t' [-Wformat]
trace.h:173:1: warning: format '%d' expects argument of type 'int',
	but argument 3 has type 'size_t' [-Wformat]
trace.h:193:1: warning: format '%d' expects argument of type 'int',
	but argument 5 has type 'size_t' [-Wformat]
trace.h:221:1: warning: format '%d' expects argument of type 'int',
	but argument 5 has type 'size_t' [-Wformat]

Fix them by using %zd.

Reported-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>