plfxlc: fix le16_to_cpu warning for beacon_interval

Fix the following sparse warnings:
drivers/net/wireless/purelifi/plfxlc/chip.c:36:31: sparse: expected unsigned short [usertype] beacon_interval
drivers/net/wireless/purelifi/plfxlc/chip.c:36:31: sparse: got restricted __le16 [usertype]

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Srinivasan Raju <srini.raju@purelifi.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220502150133.6052-1-srini.raju@purelifi.com