staging:rtl8192u: Rename ISR_BcnTimerIntr - Style

Rename the bit definition ISR_BcnTimerIntr to ISR_BCN_TIMER_INTR. This
change clears the checkpatch issue with CamelCase naming. The change is
purely a style change and should not impact runtime code execution.

Signed-off-by: John Whitmore <johnfwhitmore@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>