staging: sm750fb: rename snake case variables

Replaces CamelCase variable names with snake_case:
- dprBase -> dpr_base
- dpPortBase -> dp_port_base

Signed-off-by: Yiming Qian <qianym1996@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/20250909060130.12919-3-qianym1996@gmail.com


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