staging:rtl8192u: Rename DOT11D_GetMaxTxPwrInDbm - Style

The function DOT11D_GetMaxTxPwrInDbm causes a checkpatch issue due to
its use of CamelCase naming. The function has been renamed to
dot11d_get_max_tx_pwr_in_dbm.

This is a coding style change which should have no impact on runtime
code execution.

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