staging: rtl8712: fix camel case in function r8712_generate_ie

Adhere to linux kernel coding style.

Reported by checkpatch:

CHECK: Avoid CamelCase: <beaconPeriod>

Signed-off-by: Mahak Gupta <mahak_g@cs.iitr.ac.in>
Link: https://lore.kernel.org/r/20220407120945.31030-1-mahak_g@cs.iitr.ac.in


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>