staging: sm750fb: fix CamelCase function parameter

Change function parameter in header file from powerMode to mode,
now identical to c file function declaration. Issue found by checkpatch.

Signed-off-by: Arne Petersen <petersenarne@yahoo.com>
Link: https://lore.kernel.org/r/Yq2NufHtWbuXCjWE@ubuntu


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