rsi: make rsi_dbg a regular function

This is to address reports of this:

In file included from drivers/net/wireless/rsi/rsi_mgmt.h:22:0,
                 from drivers/net/wireless/rsi/rsi_91x_core.c:17:
drivers/net/wireless/rsi/rsi_91x_core.c: In function 'rsi_dbg':
drivers/net/wireless/rsi/rsi_main.h:44:20: error: function 'rsi_dbg' can never be inlined because it uses variable argument lists
 static inline void rsi_dbg(u32 zone, const char *fmt, ...)

Signed-off-by: John W. Linville <linville@tuxdriver.com>